Learn JS #14

JavaScript String Methods

String methods help you to work with strings.


String Methods and Properties

Primitive values, like “John Doe”, cannot have properties or methods (because they are not objects).

But with JavaScript, methods and properties are also available to primitive values, because JavaScript treats primitive values as objects when executing methods and properties.


JavaScript String Length

The length property returns the length of a string:

Example

let txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
let length = txt.length;

Extracting String Parts

There are 3 methods for extracting a part of a string:

  • slice(startend)
  • substring(startend)
  • substr(startlength)

JavaScript String slice()

slice() extracts a part of a string and returns the extracted part in a new string.

The method takes 2 parameters: the start position, and the end position (end not included).

Example

Slice out a portion of a string from position 7 to position 13 (13 not included):

let str = "Apple, Banana, Kiwi";
let part = str.slice(713);

Note: JavaScript counts positions from zero. First position is 0. Second position is 1.

If a parameter is negative, the position is counted from the end of the string.

This example slices out a portion of a string from position -12 to position -6:

Example

let str = "Apple, Banana, Kiwi";
let part = str.slice(-12, -6);

If you omit the second parameter, the method will slice out the rest of the string:

Example

let part = str.slice(7);

or, counting from the end:

Example

let part = str.slice(-12);

JavaScript String substring()

substring() is similar to slice().

The difference is that start and end values less than 0 are treated as 0 in substring().

Example

let str = "Apple, Banana, Kiwi";
let part = str.substring(713);

If you omit the second parameter, substring() will slice out the rest of the string.


JavaScript String substr()

substr() is similar to slice().

The difference is that the second parameter specifies the length of the extracted part.

Example

let str = "Apple, Banana, Kiwi";
let part = str.substr(76);

If you omit the second parameter, substr() will slice out the rest of the string.

Example

let str = "Apple, Banana, Kiwi";
let part = str.substr(7);

If the first parameter is negative, the position counts from the end of the string.

Example

let str = "Apple, Banana, Kiwi";
let part = str.substr(-4);

Replacing String Content

The replace() method replaces a specified value with another value in a string:

Example

let text = "Please visit Microsoft!";
let newText = text.replace("Microsoft""apostube");

Note:

  • The replace() method does not change the string it is called on.
  • The replace() method returns a new string.
  • The replace() method replaces only the first match
  • If you want to replace all matches, use a regular expression with the /g flag set. See examples below.

By default, the replace() method replaces only the first match:

Example

let text = "Please visit Microsoft and Microsoft!";
let newText = text.replace("Microsoft""apostube");

By default, the replace() method is case sensitive. Writing MICROSOFT (with upper-case) will not work:

Example

let text = "Please visit Microsoft!";
let newText = text.replace("MICROSOFT""apostube");

To replace case insensitive, use a regular expression with an /i flag (insensitive):

Example

let text = "Please visit Microsoft!";
let newText = text.replace(/MICROSOFT/i"apostube");

To replace all matches, use a regular expression with a /g flag (global match):

Example

let text = "Please visit Microsoft and Microsoft!";
let newText = text.replace(/Microsoft/g"apostube");

Converting to Upper and Lower Case

A string is converted to upper case with toUpperCase():

A string is converted to lower case with toLowerCase():


JavaScript String toUpperCase()

Example

let text1 = "Hello World!";
let text2 = text1.toUpperCase();

JavaScript String toLowerCase()

Example

let text1 = "Hello World!";       // String
let text2 = text1.toLowerCase();  // text2 is text1 converted to lower

JavaScript String concat()

concat() joins two or more strings:

Example

let text1 = "Hello";
let text2 = "World";
let text3 = text1.concat(" ", text2);

The concat() method can be used instead of the plus operator. These two lines do the same:

Example

text = "Hello" + " " + "World!";
text = "Hello".concat(" ""World!");

JavaScript String trim()

The trim() method removes whitespace from both sides of a string:

Example

let text1 = "      Hello World!      ";
let text2 = text1.trim();

JavaScript String Padding

ECMAScript 2017 added two String methods: padStart() and padEnd() to support padding at the beginning and at the end of a string.


JavaScript String padStart()

The padStart() method pads a string with another string:

Example

let text = "5";
let padded = text.padStart(4,"x");

Example

let text = "5";
let padded = text.padStart(4,"0");

Example

let numb = 5;
let text = numb.toString();
let padded = text.padStart(4,"0");

JavaScript String padEnd()

The padEnd() method pads a string with another string:

Example

let text = "5";
let padded = text.padEnd(4,"x");

Example

let text = "5";
let padded = text.padEnd(4,"0");

Example

let numb = 5;
let text = numb.toString();
let padded = text.padEnd(4,"0");

Extracting String Characters

There are 3 methods for extracting string characters:

  • charAt(position)
  • charCodeAt(position)
  • Property access [ ]

JavaScript String charAt()

The charAt() method returns the character at a specified index (position) in a string:

Example

let text = "HELLO WORLD";
let char = text.charAt(0);

JavaScript String charCodeAt()

The charCodeAt() method returns the unicode of the character at a specified index in a string:

The method returns a UTF-16 code (an integer between 0 and 65535).

Example

let text = "HELLO WORLD";
let char = text.charCodeAt(0);

Property Access

ECMAScript 5 (2009) allows property access [ ] on strings:

Example

let text = "HELLO WORLD";
let char = text[0];

Note:

Property access might be a little unpredictable:

  • It makes strings look like arrays (but they are not)
  • If no character is found, [ ] returns undefined, while charAt() returns an empty string.
  • It is read only. str[0] = “A” gives no error (but does not work!)

Example

let text = "HELLO WORLD";
text[0] = "A";    // Gives no error, but does not work

Converting a String to an Array

If you want to work with a string as an array, you can convert it to an array.


JavaScript String split()

A string can be converted to an array with the split() method:

Example

text.split(",")    // Split on commas
text.split(" ")    // Split on spaces
text.split("|")    // Split on pipe

If the separator is omitted, the returned array will contain the whole string in index [0].

If the separator is “”, the returned array will be an array of single characters:

Example

text.split("")

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