String.prototype.substr() vs String.prototype.substring()

Jasreet kaur — Tue, 12 Oct 2021 22:41:08 +0000

String.prototype.substr()

This method extracts a portion of the given string from the specified index and returns the specified number of characters

Syntax:

str.substr(start, length)

let str = "The quick brown fox jumps over the lazy dog";

console.log(str.substr(4,7))
// OUTPUT: quick b

console.log(str.substr(4))
// OUTPUT: quick brown fox jumps over the lazy dog

Parameters:

start

The starting index from where the characters will be extracted in the given string

length(Optional)

The number of characters that will be extracted from starting index onward

Parameter values:

If start is negative, the new substring will be extracted from the end of the string.

console.log(str.substr(-8,6))      
// OUTPUT:lazy d

Here, start's value is equal to subtracting its absolute value(value without negative sign) from the length of the string

//start = str.length - start's absolute value
console.log(str.length)        //43
console.log(str.length-8)      //43-8=35
console.log(str.substr(35,6))  // OUTPUT:lazy d

If the length is negative, it will be treated as zero and will return an empty string.

console.log(str.substr(4,-7))  //length=0
// OUTPUT:

If the parameters are NaN they will be treated as zero .

The start will become zero and therefore extract characters from index zero.

console.log(str.substr(NaN,7))  //start=0
// OUTPUT:The qui

The length will become zero and return an empty string.

console.log(str.substr(4,NaN))     //length=0
// OUTPUT:

String.prototype.substring()

This method returns a portion of the string between specified indexes (excluding the end-index).

Syntax : str.substring(start, end)

console.log(str.substring(4))
// OUTPUT:quick brown fox jumps over the lazy dog

console.log(str.substring(4,13))
// OUTPUT:quick bro
console.log(str.indexOf('o'))
// OUTPUT:12   
//index of last character in substring is 12           
//This shows that the end-index(13) is excluded

Parameters:

start

The starting index from where the characters will be extracted in the given string

end(Optional)

The index(excluding) upto where the characters will be extracted

Parameter values:

If any parameter is NaN or negative it is treated as zero.
If start > end then they will be swapped .i.e start will become end and end will become start.

console.log(str.substring(NaN,10))  //start=0
// OUTPUT:


console.log(str.substring(4,NaN))     
//end=0, start=4  => start=0,end=4  
//start and end gets swapped since start becomes greater than end
// OUTPUT:The quick



console.log(str.substring(-5,15))    //start=0
// OUTPUT:The quick brown


console.log(str.substring(5,-15))     
//end=0, start=5  => start=0, end=5  
//start and end gets swapped since start becomes greater than end
// OUTPUT:The q

DEV Community: Jasreet kaur

String.prototype.substr() vs String.prototype.substring()

String.prototype.substr()

Syntax:

Parameters:

Parameter values:

String.prototype.substring()

Syntax : str.substring(start, end)

Parameters:

Parameter values: