8: More Functions

8: More Functions

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What’s New in PHP 8 (Features, Improvements, and the JIT Compiler)

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Read the functional assessment matrix of Joseph’s behavior. Why do you think Joseph makes sarcastic, teasing comments during class? Explain your reasoning.

ABC analysis: 9 out of 10 comments were reinforced by laughing or attention from classmates.

Ms. Rollison interview: “Joseph seems to enjoy the attention from his classmates.”

Joseph interview: “I like making people laugh. It makes me feel like people like me.”

Rating scale: Attention ranked very high.

Kathleen Lane, PhD
Professor of Special Education
University of Kansas

Transcript: Kathleen Lane, PhD

Now that you’ve had a chance to practice completing a function matrix with Joseph’s data, you can see that this is a really clear-cut case. And as you look at this you can see that Joseph’s target behavior is maintained by access to attention. And as you look at the specific information in the box we can see that the teacher interview makes it clear that he enjoys attention from his classmates. Joseph himself says quite honestly, “I like making people laugh, it makes me feel like people like me.” And on the behavior rating scale, “attention” ranked very high as well and as you looked at the ABC data that were collected there were ten instances in which he was accessing peer attention for exhibiting his target behavior. So nine out of ten comments were reinforced by laughing or attention from classmates. And you can summarize data this way by saying, “9 out 10,” or if you wanted to you could actually write the number that corresponded to each instance of the target behavior in that box.

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Variables declared within a JavaScript function, become LOCAL to the function.

Local variables can only be accessed from within the function.


// code here can NOT use carName

function myFunction() <
let carName = "Volvo"
// code here CAN use carName

// code here can NOT use carName

Since local variables are only recognized inside their functions, variables with the same name can be used in different functions.

Local variables are created when a function starts, and deleted when the function is completed.

8: More Functions

As in almost any programming language, you can use functions to group pieces of code in a more logical way or practice the divine art of recursion.

Declaring a function is just a matter of writing function my_func < my_code >.

Calling a function is just like calling another program, you just write its name.

Lines 2-4 contain the 'quit' function. Lines 5-7 contain the 'hello' function If you are not absolutely sure about what this script does, please try it!.

Notice that a functions don't need to be declared in any specific order.

When running the script you'll notice that first: the function 'hello' is called, second the 'quit' function, and the program never reaches line 10.

This script is almost identically to the previous one. The main difference is the funcion 'e'. This function, prints the first argument it receives. Arguments, within funtions, are treated in the same manner as arguments given to the script. Next Previous Contents

8: More Functions

Functions are the basic building block of any application, whether they’re local functions, imported from another module, or methods on a class. They’re also values, and just like other values, TypeScript has many ways to describe how functions can be called. Let’s learn about how to write types that describe functions.

Function Type Expressions

The simplest way to describe a function is with a function type expression. These types are syntactically similar to arrow functions:

The syntax (a: string) => void means “a function with one parameter, named a , of type string, that doesn’t have a return value”. Just like with function declarations, if a parameter type isn’t specified, it’s implicitly any .

Note that the parameter name is required. The function type (string) => void means “a function with a parameter named string of type any “!

Of course, we can use a type alias to name a function type:

In JavaScript, functions can have properties in addition to being callable. However, the function type expression syntax doesn’t allow for declaring properties. If we want to describe something callable with properties, we can write a call signature in an object type:

Note that the syntax is slightly different compared to a function type expression - use : between the parameter list and the return type rather than => .

JavaScript functions can also be invoked with the new operator. TypeScript refers to these as constructors because they usually create a new object. You can write a construct signature by adding the new keyword in front of a call signature:

Some objects, like JavaScript’s Date object, can be called with or without new . You can combine call and construct signatures in the same type arbitrarily:

It’s common to write a function where the types of the input relate to the type of the output, or where the types of two inputs are related in some way. Let’s consider for a moment a function that returns the first element of an array:

This function does its job, but unfortunately has the return type any . It’d be better if the function returned the type of the array element.

In TypeScript, generics are used when we want to describe a correspondence between two values. We do this by declaring a type parameter in the function signature:

By adding a type parameter Type to this function and using it in two places, we’ve created a link between the input of the function (the array) and the output (the return value). Now when we call it, a more specific type comes out:

Note that we didn’t have to specify Type in this sample. The type was inferred - chosen automatically - by TypeScript.

We can use multiple type parameters as well. For example, a standalone version of map would look like this:

Note that in this example, TypeScript could infer both the type of the Input type parameter (from the given string array), as well as the Output type parameter based on the return value of the function expression ( number ).

We’ve written some generic functions that can work on any kind of value. Sometimes we want to relate two values, but can only operate on a certain subset of values. In this case, we can use a constraint to limit the kinds of types that a type parameter can accept.

Let’s write a function that returns the longer of two values. To do this, we need a length property that’s a number. We constrain the type parameter to that type by writing an extends clause:

There are few interesting things to note in this example. We allowed TypeScript to infer the return type of longest . Return type inference also works on generic functions.

Because we constrained Type to < length: number >, we were allowed to access the .length property of the a and b parameters. Without the type constraint, we wouldn’t be able to access those properties because the values might have been some other type without a length property.

The types of longerArray and longerString were inferred based on the arguments. Remember, generics are all about relating two or more values with the same type!

Finally, just as we’d like, the call to longest(10, 100) is rejected because the number type doesn’t have a .length property.

Working with Constrained Values

Here’s a common error when working with generic constraints:

It might look like this function is OK - Type is constrained to < length: number >, and the function either returns Type or a value matching that constraint. The problem is that the function promises to return the same kind of object as was passed in, not just some object matching the constraint. If this code were legal, you could write code that definitely wouldn’t work:

Specifying Type Arguments

TypeScript can usually infer the intended type arguments in a generic call, but not always. For example, let’s say you wrote a function to combine two arrays:

Normally it would be an error to call this function with mismatched arrays:

If you intended to do this, however, you could manually specify Type :

Guidelines for Writing Good Generic Functions

Writing generic functions is fun, and it can be easy to get carried away with type parameters. Having too many type parameters or using constraints where they aren’t needed can make inference less successful, frustrating callers of your function.

Push Type Parameters Down

Here are two ways of writing a function that appear similar:

These might seem identical at first glance, but firstElement1 is a much better way to write this function. Its inferred return type is Type , but firstElement2 ’s inferred return type is any because TypeScript has to resolve the arr[0] expression using the constraint type, rather than “waiting” to resolve the element during a call.

Rule: When possible, use the type parameter itself rather than constraining it

Use Fewer Type Parameters

Here’s another pair of similar functions:

We’ve created a type parameter Func that doesn’t relate two values. That’s always a red flag, because it means callers wanting to specify type arguments have to manually specify an extra type argument for no reason. Func doesn’t do anything but make the function harder to read and reason about!

Rule: Always use as few type parameters as possible

Type Parameters Should Appear Twice

Sometimes we forget that a function might not need to be generic:

We could just as easily have written a simpler version:

Remember, type parameters are for relating the types of multiple values. If a type parameter is only used once in the function signature, it’s not relating anything.

Rule: If a type parameter only appears in one location, strongly reconsider if you actually need it

Functions in JavaScript often take a variable number of arguments. For example, the toFixed method of number takes an optional digit count:

We can model this in TypeScript by marking the parameter as optional with ? :

Although the parameter is specified as type number , the x parameter will actually have the type number | undefined because unspecified parameters in JavaScript get the value undefined .

You can also provide a parameter default:

Now in the body of f , x will have type number because any undefined argument will be replaced with 10 . Note that when a parameter is optional, callers can always pass undefined , as this simply simulates a “missing” argument:

Optional Parameters in Callbacks

Once you’ve learned about optional parameters and function type expressions, it’s very easy to make the following mistakes when writing functions that invoke callbacks:

What people usually intend when writing index? as an optional parameter is that they want both of these calls to be legal:

What this actually means is that callback might get invoked with one argument. In other words, the function definition says that the implementation might look like this:

In turn, TypeScript will enforce this meaning and issue errors that aren’t really possible:

In JavaScript, if you call a function with more arguments than there are parameters, the extra arguments are simply ignored. TypeScript behaves the same way. Functions with fewer parameters (of the same types) can always take the place of functions with more parameters.

When writing a function type for a callback, never write an optional parameter unless you intend to call the function without passing that argument

Some JavaScript functions can be called in a variety of argument counts and types. For example, you might write a function to produce a Date that takes either a timestamp (one argument) or a month/day/year specification (three arguments).

In TypeScript, we can specify a function that can be called in different ways by writing overload signatures. To do this, write some number of function signatures (usually two or more), followed by the body of the function:

In this example, we wrote two overloads: one accepting one argument, and another accepting three arguments. These first two signatures are called the overload signatures.

Then, we wrote a function implementation with a compatible signature. Functions have an implementation signature, but this signature can’t be called directly. Even though we wrote a function with two optional parameters after the required one, it can’t be called with two parameters!

Overload Signatures and the Implementation Signature

This is a common source of confusion. Often people will write code like this and not understand why there is an error:

Again, the signature used to write the function body can’t be “seen” from the outside.

The signature of the implementation is not visible from the outside. When writing an overloaded function, you should always have two or more signatures above the implementation of the function.

The implementation signature must also be compatible with the overload signatures. For example, these functions have errors because the implementation signature doesn’t match the overloads in a correct way:

Like generics, there are a few guidelines you should follow when using function overloads. Following these principles will make your function easier to call, easier to understand, and easier to implement.

Let’s consider a function that returns the length of a string or an array:

This function is fine we can invoke it with strings or arrays. However, we can’t invoke it with a value that might be a string or an array, because TypeScript can only resolve a function call to a single overload:

Because both overloads have the same argument count and same return type, we can instead write a non-overloaded version of the function:

This is much better! Callers can invoke this with either sort of value, and as an added bonus, we don’t have to figure out a correct implementation signature.

Always prefer parameters with union types instead of overloads when possible

Declaring this in a Function

TypeScript will infer what the this should be in a function via code flow analysis, for example in the following:

TypeScript understands that the function user.becomeAdmin has a corresponding this which is the outer object user . this , heh, can be enough for a lot of cases, but there are a lot of cases where you need more control over what object this represents. The JavaScript specification states that you cannot have a parameter called this , and so TypeScript uses that syntax space to let you declare the type for this in the function body.

This pattern is common with callback-style APIs, where another object typically controls when your function is called. Note that you need to use function and not arrow functions to get this behavior:

Other Types to Know About

There are some additional types you’ll want to recognize that appear often when working with function types. Like all types, you can use them everywhere, but these are especially relevant in the context of functions.

void represents the return value of functions which don’t return a value. It’s the inferred type any time a function doesn’t have any return statements, or doesn’t return any explicit value from those return statements:

In JavaScript, a function that doesn’t return any value will implicitly return the value undefined . However, void and undefined are not the same thing in TypeScript. There are further details at the end of this chapter.

void is not the same as undefined .

The special type object refers to any value that isn’t a primitive ( string , number , boolean , symbol , null , or undefined ). This is different from the empty object type < >, and also different from the global type Object . It’s very likely you will never use Object .

object is not Object . Always use object !

Note that in JavaScript, function values are objects: They have properties, have Object.prototype in their prototype chain, are instanceof Object , you can call Object.keys on them, and so on. For this reason, function types are considered to be object s in TypeScript.

The unknown type represents any value. This is similar to the any type, but is safer because it’s not legal to do anything with an unknown value:

This is useful when describing function types because you can describe functions that accept any value without having any values in your function body.

Conversely, you can describe a function that returns a value of unknown type:

Some functions never return a value:

The never type represents values which are never observed. In a return type, this means that the function throws an exception or terminates execution of the program.

never also appears when TypeScript determines there’s nothing left in a union.

The global type Function describes properties like bind , call , apply , and others present on all function values in JavaScript. It also has the special property that values of type Function can always be called these calls return any :

This is an untyped function call and is generally best avoided because of the unsafe any return type.

If you need to accept an arbitrary function but don’t intend to call it, the type () => void is generally safer.

Rest Parameters and Arguments

In addition to using optional parameters or overloads to make functions that can accept a variety of fixed argument counts, we can also define functions that take an unbounded number of arguments using rest parameters.

A rest parameter appears after all other parameters, and uses the . syntax:

In TypeScript, the type annotation on these parameters is implicitly any[] instead of any , and any type annotation given must be of the form Array<T> or T[] , or a tuple type (which we’ll learn about later).

Conversely, we can provide a variable number of arguments from an array using the spread syntax. For example, the push method of arrays takes any number of arguments:

Note that in general, TypeScript does not assume that arrays are immutable. This can lead to some surprising behavior:

The best fix for this situation depends a bit on your code, but in general a const context is the most straightforward solution:

Using rest arguments may require turning on downlevelIteration when targeting older runtimes.

You can use parameter destructuring to conveniently unpack objects provided as an argument into one or more local variables in the function body. In JavaScript, it looks like this:

The type annotation for the object goes after the destructuring syntax:

This can look a bit verbose, but you can use a named type here as well:

Assignability of Functions

The void return type for functions can produce some unusual, but expected behavior.

Contextual typing with a return type of void does not force functions to not return something. Another way to say this is a contextual function type with a void return type ( type vf = () => void ), when implemented, can return any other value, but it will be ignored.

Thus, the following implementations of the type () => void are valid:

And when the return value of one of these functions is assigned to another variable, it will retain the type of void :

This behavior exists so that the following code is valid even though Array.prototype.push returns a number and the Array.prototype.forEach method expects a function with a return type of void .

There is one other special case to be aware of, when a literal function definition has a void return type, that function must not return anything.

For more on void please refer to these other documentation entries:


Understand how TypeScript uses JavaScript knowledge to reduce the amount of type syntax in your projects.

Object Types

How TypeScript describes the shapes of JavaScript objects.

The TypeScript docs are an open source project. Help us improve these pages by sending a Pull Request ❤

The Anonymous Functions

These functions are called anonymous because they are not declared in the standard manner by using the def keyword. You can use the lambda keyword to create small anonymous functions.

Lambda forms can take any number of arguments but return just one value in the form of an expression. They cannot contain commands or multiple expressions.

An anonymous function cannot be a direct call to print because lambda requires an expression

Lambda functions have their own local namespace and cannot access variables other than those in their parameter list and those in the global namespace.

Although it appears that lambda's are a one-line version of a function, they are not equivalent to inline statements in C or C++, whose purpose is by passing function stack allocation during invocation for performance reasons.

To protect from accidentally changing a reference parameter, when we really want it not to be changed (we just want to save time/memory) we can use the C keyword const. For example:

If a function does not return a value, then a special "TYPE" is used to tell the computer this. The return type is "void" (all lower case).

Void functions are mostly used in two classes of functions.

The first is a function that prints information for the user to read. For example (for our purposes), the printf function is treated as a void function. (In actuality, printf returns an integer which is the number of characters printed. but we almost always ignore this value.)

The brainstem is composed of the midbrain and portions of the hindbrain, specifically the pons and medulla. A major function of the midbrain is to connect the three major brain divisions: forebrain, midbrain, and hindbrain.

Major structures of the midbrain include the tectum and cerebral peduncle. The tectum is composed of rounded bulges of brain matter that are involved in visual and auditory reflexes. The cerebral peduncle consists of large bundles of nerve fiber tracts that connect the forebrain to the hindbrain.

The hindbrain is composed of two subregions known as the metencephalon and myelencephalon. The metencephalon is composed of the pons and cerebellum. The pons assists in the regulation of breathing, as well as states of sleep and arousal.

The cerebellum relays information between muscles and the brain. The myelencephalon consists of the medulla oblongata and functions to connect the spinal cord with higher brain regions. The medulla also helps to regulate autonomic functions, such as breathing and blood pressure.

What are the main functions of the muscular system?

The muscular system consists of various types of muscle that each play a crucial role in the function of the body.

Muscles allow a person to move, speak, and chew. They control heartbeat, breathing, and digestion. Other seemingly unrelated functions, including temperature regulation and vision, also rely on the muscular system.

Keep reading to discover much more about the muscular system and how it controls the body.

Share on Pinterest The muscles account for around 40 percent of a person’s weight with the largest muscle in the body being the gluteus maximus in the buttocks.

The muscular system contains more than 600 muscles that work together to enable the full functioning of the body.

There are 3 types of muscles in the body:

Skeletal muscle

Skeletal muscles are the only muscles that can be consciously controlled. They are attached to bones, and contracting the muscles causes movement of those bones.

Any action that a person consciously undertakes involves the use of skeletal muscles. Examples of such activities include running, chewing, and writing.

Smooth muscle

Smooth muscle lines the inside of blood vessels and organs, such as the stomach, and is also known as visceral muscle.

It is the weakest type of muscle but has an essential role in moving food along the digestive tract and maintaining blood circulation through the blood vessels.

Smooth muscle acts involuntarily and cannot be consciously controlled.

Cardiac muscle

Located only in the heart, cardiac muscle pumps blood around the body. Cardiac muscle stimulates its own contractions that form our heartbeat. Signals from the nervous system control the rate of contraction. This type of muscle is strong and acts involuntarily.

The main functions of the muscular system are as follows:

1. Mobility

The muscular system’s main function is to allow movement. When muscles contract, they contribute to gross and fine movement.

Gross movement refers to large, coordinated motions and includes:

Fine movement involves smaller movements, such as:

The smaller skeletal muscles are usually responsible for this type of action.

Most muscle movement of the body is under conscious control. However, some movements are reflexive, such as withdrawing a hand from a source of heat.

2. Stability

Muscle tendons stretch over joints and contribute to joint stability. Muscle tendons in the knee joint and the shoulder joint are crucial in stabilization.

The core muscles are those in the abdomen, back, and pelvis, and they also stabilize the body and assist in tasks, such as lifting weights.

3. Posture

Skeletal muscles help keep the body in the correct position when someone is sitting or standing. This is known as posture.

Good posture relies on strong, flexible muscles. Stiff, weak, or tight muscles contribute to poor posture and misalignment of the body.

Long-term, bad posture leads to joint and muscle pain in the shoulders, back, neck, and elsewhere.

4. Circulation

The heart is a muscle that pumps blood throughout the body. The movement of the heart is outside of conscious control, and it contracts automatically when stimulated by electrical signals.

Smooth muscle in the arteries and veins plays a further role in the circulation of blood around the body. These muscles maintain blood pressure and circulation in the event of blood loss or dehydration.

They expand to increase blood flow during times of intense exercise when the body requires more oxygen.

5. Respiration

Breathing involves the use of the diaphragm muscle.

The diaphragm is a dome-shaped muscle located below the lungs. When the diaphragm contracts, it pushes downward, causing the chest cavity to get bigger. The lungs then fill with air. When the diaphragm muscle relaxes, it pushes air out of the lungs.

When someone wants to breath more deeply, it requires help from other muscles, including those in the abdomen, back, and neck.

6. Digestion

Smooth muscles in the gastrointestinal or GI tract control digestion. The GI tract stretches from the mouth to the anus.

Food moves through the digestive system with a wave-like motion called peristalsis. Muscles in the walls of the hollow organs contract and relax to cause this movement, which pushes food through the esophagus into the stomach.

The upper muscle in the stomach relaxes to allow food to enter, while the lower muscles mix food particles with stomach acid and enzymes.

The digested food moves from the stomach to the intestines by peristalsis. From here, more muscles contract to pass the food out of the body as stool.

7. Urination

The urinary system comprises both smooth and skeletal muscles, including those in the:

  • bladder
  • kidneys
  • penis or vagina
  • prostate
  • ureters
  • urethra

The muscles and nerves must work together to hold and release urine from the bladder.

Urinary problems, such as poor bladder control or retention of urine, are caused by damage to the nerves that carry signals to the muscles.

8. Childbirth

Smooth muscles in the uterus expand and contract during childbirth. These movements push the baby through the vagina. Also, the pelvic floor muscles help to guide the baby’s head down the birth canal.

9. Vision

Six skeletal muscles around the eye control its movements. These muscles work quickly and precisely, and allow the eye to:

If someone experiences damage to their eye muscles, it can impair their vision.

10. Organ protection

Muscles in the torso protect the internal organs at the front, sides, and back of the body. The bones of the spine and the ribs provide further protection.

Muscles also protect the bones and organs by absorbing shock and reducing friction in the joints.

11. Temperature regulation

Maintaining normal body temperature is an important function of the muscular system. Almost 85 percent of the heat a person generates in their body comes from contracting muscles.

When body heat falls below optimal levels, the skeletal muscles increase their activity to make heat. Shivering is one example of this mechanism. Muscles in the blood vessels also contract to maintain body heat.

Body temperature can be brought back within normal range through the relaxation of smooth muscle in the blood vessels. This action increases blood flow and releases excess heat through the skin.

  1. Muscles make up approximately 40 percent of total weight.
  2. The heart is the hardest-working muscle in the body. It pumps 5 quarts of blood per minute and 2,000 gallons daily.
  3. The gluteus maximus is the body’s largest muscle. It is in the buttocks and helps humans maintain an upright posture.
  4. The ear contains the smallest muscles in the body alongside the smallest bones. These muscles hold the inner ear together and are connected to the eardrum.
  5. A muscle called the masseter in the jaw is the strongest muscle by weight. It allows the teeth to close with a force of up to 55 pounds on the incisors or 200 pounds on the molars.

Below is a 3-D model of the muscular system, which is fully interactive.

Explore the model, using your mouse pad or touchscreen, to understand more about the muscular system.

Muscles play a part in all functions of the body, from heartbeat and breathing to running and jumping. When muscles become damaged, it can impact movement, speech, and much more.

Several conditions, including fibromyalgia, multiple sclerosis , and Parkinson’s disease, interfere with the smooth running of the muscular system.

A person should see a doctor if they notice signs of muscular weakness or pain that they cannot explain. A doctor can decide the problem and come up with an appropriate treatment plan.

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