JS Tutorials
JS Introduction
JS Syntax
JS Comments
JS Variables
JS Operators
JS Data Types
JS Functions
JS Objects
JS Numbers
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JS Array Methods
JS Booleans
JS Events
JS Strings
JS Dates
JS Maths
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Object Definition
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JS Functions
Function Definition
Function Parameters
Function Invocation
Function Call
Function Apply
Function ClosuresJS Classes
Class Intro
Class Inheritance
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JS Async
JS Callbacks
JS Aysnchronous
JS Promises
JS Sync/Await
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JavaScript Callbacks
Function Sequence
JavaScript functions are executed in the sequence they are called. Not in the sequence they are defined.
The JavaScript apply() Method
The apply() method is similar to the call() method (previous chapter).
In this example the fullName method of person is applied on person1:
Example
function myFirst() {
myDisplayer("Hello");
}
function
mySecond() {
myDisplayer("Goodbye");
}
myFirst();
mySecond();
Sequence Control
The difference is:
Sometimes you would like to have better control over when to execute a function.
Suppose you want to do a calculation, and then display the result.
call() method takes arguments
separately.
You could call a calculator function ( myCalculator ) , save the result, and then call another function
(myDisplayer) to display the result:
Example
document.getElementById("demo").innerHTML = some;
}
function myCalculator(num1, num2) {
let sum = num1 + num2;
return sum;
}
let result = myCalculator(5, 5);
myDisplayer(result);
JavaScript Callbacks
A callback is a function passed as an argument to another function.
Using a callback, you could call the calculator function (myCalculator) with a callback, and let the calculator function run the callback after the calculation is finished:
When to Use a Callback?
he examples above are not very exciting.
They are simplified to teach you the callback syntax.
Where callbacks really shine are in asynchronous functions, where one function has to wait for another function (like waiting for a file to load).
Asynchronous functions are covered in the next chapter.