JavaScript Functions

function add(a, b = 0) {
    let x = 1;
    return a + b;
}

let sum = add(1, 2); // sum = 3

• a and b are parameters
• b = 0 defines a default parameter
• let x is a local variable and is not accessible outside the function

Info

• Function declaration is hoisted to the top of the scope.
• Accessing add without () returns the function object and not the result

    let sum = add
    let result = sum(1, 2) // result = 3
  

Default Parameters

function add(a = 0, b = 0) {
    return a + b;
}

Rest Parameters

function add(...numbers) {
    let sum = 0;
    for (let number of numbers) {
        sum += number;
    }
    return sum;
}

this in Functions

const person = {
    name: "John",
    age: 30,
    greet: function () {
        console.log(`Hello, my name is ${this.name}`);
    },
};

person.greet(); // Hello, my name is John

• this refers to the object that called the function
• bind, call and apply can be used to change the this value

Arrow Function

let add = (a, b) => a + b;
let sum = add(1, 2); // sum = 3

JS Default Functions

• alert() - displays an alert box with a message and an OK button
• console.log() - writes a message to the console
• eval() - evaluates a string as a JavaScript expression
• isFinite() - determines whether a number is finite
• isNaN() - determines whether a value is NaN
• parseFloat() - parses a string and returns a floating point number
• encodeURI() - encodes a URI
• decodeURI() - decodes a URI
• setTimeout() - calls a function after a specified number of milliseconds
• setInterval() - calls a function repeatedly, after a specified number of milliseconds

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