The replace()
method returns a new string with some or all matches of a pattern
replaced by a replacement
. The pattern
can be a string or a RegExp, and the replacement
can be a string or a function to be called for each match.
str.replace(regexp|substr, newSubStr|function[, flags])
regexp (pattern)
substr (pattern)
newSubStr
.newSubStr (replacement)
function (replacement)
i
m
A new string with some or all matches of a pattern replaced by a replacement.
This method does not change the String object it is called on. It simply returns a new string.
To perform a global search and replace, either include the g
switch in the regular expression or if the first parameter is a string, include g
in the flags
parameter.
The replacement string can include the following special replacement patterns:
Pattern | Inserts |
$ |
Inserts a "$". |
@DATA@amp; |
Inserts the matched substring. |
|
Inserts the portion of the string that precedes the matched substring. |
|
Inserts the portion of the string that follows the matched substring. |
$n or $nn |
Where n or nn are decimal digits, inserts the nth parenthesized submatch string, provided the first argument was a RegExp object. |
You can specify a function as the second parameter. In this case, the function will be invoked after the match has been performed. The function's result (return value) will be used as the replacement string. (Note: the above-mentioned special replacement patterns do not apply in this case.) Note that the function will be invoked multiple times for each full match to be replaced if the regular expression in the first parameter is global.
The arguments to the function are as follows:
Possible name | Supplied value |
match |
The matched substring. (Corresponds to @DATA@amp; above.) |
p1, p2, ... |
The nth parenthesized submatch string, provided the first argument to replace() was a RegExp object. (Corresponds to $1 , $2 , etc. above.) For example, if /(\a+)(\b+)/ , was given, p1 is the match for \a+ , and p2 for \b+ . |
offset |
The offset of the matched substring within the total string being examined. (For example, if the total string was 'abcd' , and the matched substring was 'bc' , then this argument will be 1.) |
string |
The total string being examined. |
(The exact number of arguments will depend on whether the first argument was a RegExp object and, if so, how many parenthesized submatches it specifies.)
The following example will set newString
to 'abc - 12345 - #$*%'
:
function replacer(match, p1, p2, p3, offset, string) { // p1 is nondigits, p2 digits, and p3 non-alphanumerics return [p1, p2, p3].join(' - '); } var newString = 'abc12345#$*%'.replace(/([^\d]*)(\d*)([^\w]*)/, replacer);
global
and ignore
with replace()
In the following example, the regular expression includes the global and ignore case flags which permits replace()
to replace each occurrence of 'apples' in the string with 'oranges'.
var re = /apples/gi; var str = 'Apples are round, and apples are juicy.'; var newstr = str.replace(re, 'oranges'); console.log(newstr); // oranges are round, and oranges are juicy.
This logs 'oranges are round, and oranges are juicy'.
replace()
In the following example, the regular expression is defined in replace()
and includes the ignore case flag.
var str = 'Twas the night before Xmas...'; var newstr = str.replace(/xmas/i, 'Christmas'); console.log(newstr); // Twas the night before Christmas...
This logs 'Twas the night before Christmas...'
The following script switches the words in the string. For the replacement text, the script uses the $1
and $2
replacement patterns.
var re = /(\w+)\s(\w+)/; var str = 'John Smith'; var newstr = str.replace(re, '$2, $1'); console.log(newstr); // Smith, John
This logs 'Smith, John'.
In this example, all occurrences of capital letters in the string are converted to lower case, and a hyphen is inserted just before the match location. The important thing here is that additional operations are needed on the matched item before it is given back as a replacement.
The replacement function accepts the matched snippet as its parameter, and uses it to transform the case and concatenate the hyphen before returning.
function styleHyphenFormat(propertyName) { function upperToHyphenLower(match) { return '-' + match.toLowerCase(); } return propertyName.replace(/[A-Z]/g, upperToHyphenLower); }
Given styleHyphenFormat('borderTop')
, this returns 'border-top'.
Because we want to further transform the result of the match before the final substitution is made, we must use a function. This forces the evaluation of the match prior to the toLowerCase() method. If we had tried to do this using the match without a function, the toLowerCase() would have no effect.
var newString = propertyName.replace(/[A-Z]/g, '-' + '@DATA@amp;'.toLowerCase()); // won't work
This is because '@DATA@amp;'.toLowerCase()
would be evaluated first as a string literal (resulting in the same '@DATA@amp;'
) before using the characters as a pattern.
The following example replaces a Fahrenheit degree with its equivalent Celsius degree. The Fahrenheit degree should be a number ending with F. The function returns the Celsius number ending with C. For example, if the input number is 212F, the function returns 100C. If the number is 0F, the function returns -17.77777777777778C.
The regular expression test
checks for any number that ends with F. The number of Fahrenheit degree is accessible to the function through its second parameter, p1
. The function sets the Celsius number based on the Fahrenheit degree passed in a string to the f2c()
function. f2c()
then returns the Celsius number. This function approximates Perl's s///e
flag.
function f2c(x) { function convert(str, p1, offset, s) { return ((p1 - 32) * 5/9) + 'C'; } var s = String(x); var test = /(\d+(?:\.\d*)?)F\b/g; return s.replace(test, convert); }
for
loopsThe following example takes a string pattern and converts it into an array of objects.
Input:
A string made out of the characters x
, -
and _
x-x_ x---x---x---x--- x-xxx-xx-x- x_x_x___x___x___
Output:
An array of objects. An 'x'
denotes an 'on'
state, a '-'
(hyphen) denotes an 'off'
state and an '_'
(underscore) denotes the length of an 'on'
state.
[ { on: true, length: 1 }, { on: false, length: 1 }, { on: true, length: 2 } ... ]
Snippet:
var str = 'x-x_'; var retArr = []; str.replace(/(x_*)|(-)/g, function(match, p1, p2) { if (p1) { retArr.push({ on: true, length: p1.length }); } if (p2) { retArr.push({ on: false, length: 1 }); } }); console.log(retArr);
This snippet generates an array of 3 objects in the desired format without using a for
loop.
replace()
is called with a global regular expression, the RegExp.lastIndex property (if specified) will be reset to 0
().flags
argument is deprecated and throws a console warning ().Created by Mozilla Contributors, license: CC-BY-SA 2.5