Padding a String to a Certain Length with Another String
Summary: in this tutorial, you will learn how to pad a string with another string to a certain length.
String.prototype.padStart()
The padStart() method pads a string with another string to a certain length from the start of the string and returns a resulting string that reaches a certain length. The following illustrates the padStart() method:
String.prototype.padStart(padLength [,padString]);
Code language: CSS (css)
The padStart() method takes two parameters:
- The
padLengthis the length of the resulting string once it is padded. If thepadLengthis less than the string’s length, the string is returned as-is without padding. - The
padStringis an optional argument which is used to pad the string. The default value for this parameter is ‘ ‘. If thepadStringis greater thanpadLength, thepadStringwill be truncated and only the left-most part will be padded.
String.prototype.padStart() examples
Suppose, you want a numeric string with 8 characters. For the string whose length is less than 8, it will be padded with zeros (0).
let str = '1234'.padStart(8,'0');
console.log(str); // "00001234"
Code language: JavaScript (javascript)
The following example pads a string by spaces because we don’t pass the pad string.
let str = 'abc'.padStart(5);
console.log(str); // " abc"
Code language: JavaScript (javascript)
String.prototype.padEnd()
Similar to the padStart() method, the padEnd() method pads a string to a certain length with another string. However, the padEnd() method pads from the end of the string. The following shows the syntax of the padEnd() method:
String.prototype.padEnd(padLength [,padString]);
Code language: CSS (css)
String.prototype.padEnd() examples
See the following example:
let str = 'abc'.padEnd(5);
console.log(str); // "abc "
Code language: JavaScript (javascript)
In this example, because we did not provide the second argument, the padEnd() method uses the space ' ' to pad the 'abc' string. Here is another example:
str = 'abc'.padEnd(5,'*');
console.log(str); // "abc**"
Code language: JavaScript (javascript)
In this example, we use the * string as the second argument, the resulting string was padded by two * strings to make its length 5. And another example:
str = 'abc'.padEnd(5,'def');
console.log(str); // "abcde"
Code language: JavaScript (javascript)
In this example, the length of the resulting string must be 5, therefore, the pad string was truncated ("f") and only its left-most part ("de") was padded.
In this tutorial, you have learned how to pad a string to a certain length with another string using padStart() and padEnd() methods.