How to convert a string into a integer without using parseInt() function in JavaScript ?

In JavaScript, there is a simple function parseInt() to convert a string to an integer. In order to know more about the function, you can refer to this. In this article, we will learn how to convert the string to an integer without using the parseInt() function.

Advantage of parseInt() over this method. The parseInt() function converts the number which is present in any base to base 10 which is not possible using the method discusses above.

Below are the following methods:

• Using coercion
• Using the Number() function
• Using the unary + operator
• Using Math floor() Method
• Using Math.ceil( ) function

Method 1: Using coercion

The very simple idea is to multiply the string by 1. If the string contains a number it will convert to an integer otherwise NaN will be returned or we can type cast to Number.

Example:

Javascript

function convertStoI() {
    let a = "100";
    let b = a * 1;
    console.log(typeof (b));
    let d = "3 11 43" * 1;
    console.log(typeof (d));
}
convertStoI();

Output

number
number

Method 2: Using the Number() function

The Number function is used to convert the parameter to the number type.

Example:

Javascript

function convertStoI() {
    const a = "100";
    const b = Number(a);
    console.log(typeof (b));
    const d = "3 11 43" * 1;
    console.log(typeof (d));
}
convertStoI();

Output

number
number

Method 3: Using the unary + operator

If we use the ‘+’ operator before any string if the string in numeric it converts it to a number. 

Javascript

function convertStoI() {
    let a = "100";
    let b = +(a);
    console.log(typeof (b));
    let d = +"3 11 43";
    console.log(typeof (d));
}
convertStoI();

Output

number
number

Method 4: Using Math floor() Method

The Javascript Math.floor() method is used to round off the number passed as a parameter to its nearest integer in a Downward direction of rounding i.e. towards the lesser value.

Example:

Javascript

function convertStoI() {
    let a = "100";
    let b = Math.floor(a);
    console.log(typeof (b));
}
convertStoI();

Output

number

Method 5: Using Math.ceil( ) function

The Math.ceil() function in JavaScript is used to round the number passed as a parameter to its nearest integer in an Upward direction of rounding i.e. towards the greater value.

Javascript

function convertStoI() {
    let a = "100";
    let b = Math.ceil(a);
    console.log(typeof (b));
}
convertStoI();

Output

number