JavaScript String Methods
JavaScript Where To
String methods help you to work with strings.
var x = 5;
var y = 6;
var z = x + y;
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.
String Length
The length property returns the length of a string:
var txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
var sln = txt.length;
Finding a String in a String
The indexOf() method returns the index of (the position of) the first occurrence of a specified text in a string:
var str = "Please locate where 'locate' occurs!";
var pos = str.indexOf("locate");
The lastIndexOf() method returns the index of the last occurrence of a specified text in a string:
var str = "Please locate where 'locate' occurs!";
var pos = str.lastIndexOf("locate");
Both indexOf(), and lastIndexOf() return -1 if the text is not found.
var str = "Please locate where 'locate' occurs!";
var pos = str.lastIndexOf("John");
Both methods accept a second parameter as the starting position for the search:
var str = "Please locate where 'locate' occurs!";
var pos = str.indexOf("locate", 15);
The lastIndexOf() methods searches backwards (from the end to the beginning), meaning: if the second parameter is 15, the search starts at position 15, and searches to the beginning of the string.
var str = "Please locate where 'locate' occurs!";
var pos = str.lastIndexOf("locate", 15);
Searching for a String in a String
The search() method searches a string for a specified value and returns the position of the match:
var str = "Please locate where 'locate' occurs!";
var pos = str.search("locate");
Index() and search()
The two methods are NOT equal. These are the differences:
- The search() method cannot take a second start position argument
- The indexOf() method cannot take powerful search values (regular expressions).
Extracting String Parts
Thslice() 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). This example slices out a portion of a string from position 7 to position 12 (13-1):
var str = "Apple, Banana, Kiwi";
var res = str.slice(7, 13);
If a parameter is negative, the position is counted from the end of the string.
var str = "Apple, Banana, Kiwi";
var res = str.slice(-12, -6);
var res = str.slice(7, 13);
If you omit the second parameter, the method will slice out the rest of the string:
var res = str.slice(7);
The substring() Method
substring() is similar to slice(). The difference is that substring() cannot accept negative indexes. If you omit the second parameter, substring() will slice out the rest of the string.
var str = "Apple, Banana, Kiwi";
var res = str.substring(7, 13);
The substr() Method
substr() is similar to slice(). The difference is that the second parameter specifies the length of the extracted part. If you omit the second parameter, substr() will slice out the rest of the string.
var str = "Apple, Banana, Kiwi";
var res = str.substr(7, 6);
Replacing String Content
The replace() method replaces a specified value with another value in a string:
str = "Please visit Microsoft!";
var n = str.replace("Microsoft", "W3Schools");
The replace() method does not change the string it is called on. It returns a new string. By default, the replace() method replaces only the first match:
str = "Please visit Microsoft!";
var n = str.replace("Microsoft", "W3Schools");
By default, the replace() method is case sensitive. Writing MICROSOFT (with upper-case) will not work. To replace case insensitive, use a regular expression with an /i flag (insensitive):
str = "Please visit Microsoft!";
var n = str.replace(/MICROSOFT/i, "W3Schools");
Converting to Upper and Lower Case
A string is converted to upper case with toUpperCase(). A string is converted to lower case with toLowerCase():
var text1 = "Hello World!"; // String
var text2 = text1.toUpperCase(); // text2 is text1 converted to upper
The concat() Method
concat() joins two or more strings. The concat() method can be used instead of the plus operator. These two lines do the same. All string methods return a new string. They don't modify the original string. Formally said: Strings are immutable: Strings cannot be changed, only replaced
var text1 = "Hello";
var text2 = "World";
var text3 = text1.concat(" ", text2);
String.trim()
The trim() method removes whitespace from both sides of a string:
var str = " Hello World! ";
alert(str.trim());
The trim() method is not supported in Internet Explorer 8 or lower.
If you need to support IE 8, you can use replace() with a regular expression instead:
var str = " Hello World! ";
alert(str.replace(/^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g, ''));
You can also use the replace solution above to add a trim function to the JavaScript String.prototype:
if (!String.prototype.trim) {
String.prototype.trim = function () {
return this.replace(/^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g, '');
};
}
var str = " Hello World! ";
alert(str.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.
let str = "5";
str = str.padStart(4,0);
// result is 0005
Extracting String Characters
There are 3 methods for extracting string characters:
- charAt(position)
- charCodeAt(position)
- Property access [ ]
The charAt() Method
The charAt() method returns the character at a specified index (position) in a string:
var str = "HELLO WORLD";
str.charAt(0);
The charCodeAt() Method
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).
var str = "HELLO WORLD";
str.charCodeAt(0); // returns 72
Property Access
ECMAScript 5 (2009) allows property access [ ] on strings. Property access might be a little unpredictable:
- It does not work in Internet Explorer 7 or earlier
- 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!)
var str = "HELLO WORLD";
str[0];
Converting a String to an Array
A string can be converted to an array with the split() method:
var txt = "a,b,c,d,e"; // String
txt.split(","); // Split on commas
txt.split(" "); // Split on spaces
txt.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:
var txt = "Hello"; // String
txt.split(""); // Split in characters
