JavaScript to keep only first N characters in a string

In this article, we have given a string and the task is to keep only the first n characters of the string using JavaScript. There are various methods to solve this problem, some of which are discussed below: 

Methods to keep only First N characters in a String:

• Using substring() Method
• Using slice() Method
• Using JavaScript For loop

Method 1: Using substring() Method

The string.substring() method is used to return the part of the given string from the start index to the end index. Indexing starts from zero (0). 

Syntax:

string.substring(Startindex, Endindex)

Example: This example uses the above-explained approach.

javascript

// JavaScript to keep only first
// 'n' characters of String

// Original string
let str = "GeeksforGeeks";

// Keep first 5 letters
let n = 5;

console.log("Original String = " + str);
console.log("n = " + n);

// Using substring() method
str = str.substring(0, n);

console.log("Keep first " + n +
    " characters of original String = " + str);

Output

Original String = GeeksforGeeks
n = 5
Keep first 5 characters of original String = Geeks

Method 2: Using slice() Method

The string.slice() method is used to return a part or slice of the given input string. 

Syntax:

string.slice(startingindex, endingindex)

Example: This example uses slice() method to get part of a string.

javascript

// JavaScript script to keep only
// first 'n' characters of String

// Original string
let str = "Data Structure";

// Keep first 11 letters
let n = 11;

console.log("Original String = " + str);
console.log("n = " + n);

// Using slice() method
str = str.slice(0, n);

console.log("Keep first " + n +
    " characters of original String = " + str);

Output

Original String = Data Structure
n = 11
Keep first 11 characters of original String = Data Struct

Method 3: Using JavaScript For loop

Looping in programming languages is a feature that facilitates the execution of a set of instructions repeatedly until some condition evaluates and becomes false. We come across for loop which provides a brief and systematic way of writing the loop structure. 

Syntax:

for (statement 1 ; statement 2 ; statement 3){
    code here...
}

Example: In this example, we will loop till the given index and store characters in the result string.

Javascript

// JavaScript to keep only first
// 'n' characters of String

// Original string
let str = "GeeksforGeeks";

// Keep first 5 letters
let n = 5;
let res = "";
console.log("Original String = " + str);
console.log("n = " + n);

// Loop till given number of characters
for (let i = 0; i < n; i++) {
    res += str[i];
}

console.log(
    "Keep first " + n +
    " characters of original String = "
    + res
);

Output

Original String = GeeksforGeeks
n = 5
Keep first 5 characters of original String = Geeks