variable && function () /JavaScript

# Web Site Writing Basics

# javascript

# variable

# Function

The relationship between variables and functions in JavaScript is an important basis of programming. It can be summarized mainly as follows:

1. Using a variable to store the value of a function

In JavaScript, a function is a type of object (First-Class Functions). This means that it can be treated as an object or other value. This allows us to use variables to store the value of the function:

JavaScript

/ / The variable 'myFunction' stores a value that is a function.

const myFunction = function (a, b) {

return a + b;

};

/ / A function can be called through a variable.

Let result = myFunction (5, 3); / / result is 8

Benefits: Assigning a function to a variable allows a function to be sent as an argument to another function (Callbacks) or returned a function from another function (Higher-Order Functions).

2.Function uses variable (Scope)

Variables are closely related to functions through the concept of Scope:

A. Variables within a function (Local Variables)

Variables declared within a function are accessed only in that function (Local Scope) and are recreated every time the function is invoked.

JavaScript

Function calculated (x) {

/ / The variable 'y' is a variable within the function.

const y = 10;

return x + y;

}

/ / console.log (y); / / Error: y is not defined

B. External Function Variables (Global / Outer Scope Variables)

The function can access variables declared outside the function (Lexical Scope).

JavaScript

Const taxRate = 0.07; / / External variable

Function calculateTax (price) {

/ / The function can access' taxRate '.

return price * taxRate;

}

Closure: This is the most powerful relationship, when the function "remembers" and continues to access variables from the created boundary, even if the boundary has already been completed.

3.The variable is the argument and the value returned.

The function uses variables to receive input and output information:

Arguments: The variable used to receive the value sent into the function.

Return Value: The function uses the return command to send a value (which is a value stored in a variable or as a constant) back to the executed code.

JavaScript

The functions multiply (num1, num2) {/ / num1 and num2 are argument variables.

const product = num1 * num2; / / 'product' is an internal variable

Return product; / / Send back the value stored in 'product'

}

const finalAnswer = multiply (4, 5); / / 'finalAnswer' stores the returned value