Emulating SQL LIKE in JavaScript

Question

How can I emulate the SQL keyword LIKE in JavaScript?

For those of you who don't know what LIKE is, it's a very simple regex which only supports the wildcards %, which matches 0 or more characters, and _ which matches exactly one character.

However, it's not just possible to do something like:

var match = new RegEx(likeExpr.replace("%", ".*").replace("_", ".")).exec(str) != null;

...because the pattern might contain dots, stars and any other special regex characters.

Answer 1

What you have will work as long as you first escape the regex characters in your pattern. Below is one example from Simon Willison’s blog:

RegExp.escape = function(text) {
  if (!arguments.callee.sRE) {
    var specials = [
      '/', '.', '*', '+', '?', '|',
      '(', ')', '[', ']', '{', '}', '\\'
    ];
    arguments.callee.sRE = new RegExp(
      '(\\' + specials.join('|\\') + ')', 'g'
    );
  }
  return text.replace(arguments.callee.sRE, '\\$1');
}

You could then implement your code as:

likeExpr = RegExp.escape(likeExpr);
var match = new RegEx(likeExpr.replace("%", ".*").replace("_", ".")).exec(str) != null;

Answer 2

I was looking for an answer the same question and came up with this after reading Kip's reply:

String.prototype.like = function(search) {
    if (typeof search !== 'string' || this === null) {return false; }
    // Remove special chars
    search = search.replace(new RegExp("([\\.\\\\\\+\\*\\?\\[\\^\\]\\$\\(\\)\\{\\}\\=\\!\\<\\>\\|\\:\\-])", "g"), "\\$1");
    // Replace % and _ with equivalent regex
    search = search.replace(/%/g, '.*').replace(/_/g, '.');
    // Check matches
    return RegExp('^' + search + '$', 'gi').test(this);
}

You can then use it as follows (note that it ignores UPPER/lower case):

var url = 'http://www.mydomain.com/page1.aspx';
console.log(url.like('%mydomain.com/page_.asp%')); // true

NOTE 29/11/2013: Updated with RegExp.test() performance improvement as per Lucios comment below.

Answer 3

An old question but there are actually no good answers here. TSQL LIKE expressions can contain square-bracket escaped sections that are already almost valid regular expressions and allow for matching % and _. E.g.:

'75%' LIKE '75[%]'
'[foo]' LIKE '[[]foo]' -- ugh

Here's my function to convert a LIKE expression into a RegExp. The input is split into square-bracket and non-square-bracket sections. The square-bracket sections just need backslash escaping and the non-square-bracket sections are fully escaped while the % and _ directives are converted to regular expressions.

const likeRegExp = (expression, caseSensitive = false) =>
    new RegExp(`^${
        expression.split(/(\[.+?\])/g)
        .map((s, i) => i % 2 ?
            s.replace(/\\/g, '\\\\') :
            s.replace(/[-\/\\^$*+?.()|[\]{}%_]/g, m => {
                switch(m) {
                    case '%': return '.*';
                    case '_': return '.';
                    default: return `\\${m}`;
                }
            })
        ).join('')
    }$`, caseSensitive ? '' : 'i');

Answer 4

Here's a function I use, based on PHP's preg_quote function:

function regex_quote(str) {
  return str.replace(new RegExp("([\\.\\\\\\+\\*\\?\\[\\^\\]\\$\\(\\)\\{\\}\\=\\!\\<\\>\\|\\:\\-])", "g"), "\\$1");
}

So your line would now be:

var match = new RegEx(regex_quote(likeExpr).replace("%", ".*").replace("_", ".")).exec(str) != null;

Answer 5

If you want to use a regex, you can wrap each character of the string in square-brackets. Then you only have a few characters to escape.

But a better option might be to truncate the target strings so the length matches your search string and check for equality.

Answer 6

I wanted something that also handles escaping the wildcards % and _ using \% and \_.

Here is my solution using negative lookbehind:

// escapes RegExp special characters
const escapePattern = s => s.replace(/[-/\\^$*+?.()|[\]{}]/g, '\\$&');

// converts ILIKE pattern to a RegExp object
const ilikeToRegExp = pattern =>
  new RegExp(
    `^${escapePattern(pattern)}$`
      // convert ILIKE wildcards, don't match escaped
      .replace(/(?<![\\])%/g, '.*')
      .replace(/(?<![\\])_/g, '.')
      // replace ILIKE escapes
      .replace(/\\%/g, '%')
      .replace(/\\_/g, '_'),
    'i'
  );

Usage:

ilikeToRegExp('%eLlo WoR%').test('hello world')  
// true

ilikeToRegExp('ello wor').test('hello world')  
// false

ilikeToRegExp('%90\%%').test('...90%...') 
// true

Answer 7

In Chris Van Opstal's answer you should use replaceAll instead of replace to replace all occurrances of '%' and '_'. Reference to how to do replaceAll - here

Answer 8

Johnny come lately here but this works for me I use it for my spa pages to avoid certain pages showing results after the default page:

function like(haystack,needle){
    needle = needle.split(','); 
    var str = haystack.toLowerCase();
    var n = -1;
    for(var i=0;i<needle.length;i++){
        n = str.search(needle[i]);
        if(n > -1){
            return n;
        }
    }
return n;
}

usage is - here I want to not show any results on the tools,contact or home pages - results() is a function I do not show here:

var n = like($data,'tools,contact,home');
//~ alert(n);
if(n < 0){// does not match anything in the above string
  results($data);
}

Answer 9

I needed this, with escaping and working in Safari (no negative lookbehinds). Here is what I came up with:

/**
 * Quotes a string following the same rules as https://www.php.net/manual/function.preg-quote.php
 *
 * Sourced from https://locutus.io/php/preg_quote/
 *
 * @param {string} str String to quote.
 * @param {?string} [delimiter] Delimiter to also quote.
 * @returns {string} The quoted string.
 */
function regexQuote(str, delimiter) {
    return (str + '').replace(new RegExp('[.\\\\+*?\\[\\^\\]$(){}=!<>|:\\' + (delimiter || '') + '-]', 'g'), '\\$&');
}

/**
 * Removes the diacritical marks from a string.
 *
 * Diacritical marks: {@link https://unicode-table.com/blocks/combining-diacritical-marks/}
 *
 * @param {string} str The string from which to strip the diacritical marks.
 * @returns {string} Stripped string.
 */
function stripDiacriticalMarks(str) {
    return unorm.nfkd(str).replaceAll(/[\u0300-\u036f]+/g, '');
}

/**
 * Checks if the string `haystack` is like `needle`, `needle` can contain '%' and '_'
 * characters which will behave as if used in a SQL LIKE condition. Character escaping
 * is supported with '\'.
 *
 * @param {string} haystack The string to check if it is like `needle`.
 * @param {string} needle The string used to check if `haystack` is like it.
 * @param {boolean} [ai] Whether to check likeness in an accent-insensitive manner.
 * @param {boolean} [ci] Whether to check likeness in a case-insensitive manner.
 * @returns {boolean} True if `haystack` is like `needle`, otherwise, false.
 */
function strLike(haystack, needle, ai = true, ci = true) {
    if (ai) {
        haystack = stripDiacriticalMarks(haystack);
        needle = stripDiacriticalMarks(needle);
    }

    needle = regexQuote(needle, '/');

    let tokens = [];

    for (let i = 0; i < needle.length; ) {
        if (needle[i] === '\\') {
            i += 2;
            if (i < needle.length) {
                if (needle[i] === '\\') {
                    tokens.push('\\\\');
                    i += 2;
                } else {
                    tokens.push(needle[i]);
                    ++i;
                }
            } else {
                tokens.push('\\\\');
            }
        } else {
            switch (needle[i]) {
                case '_':
                    tokens.push('.')
                    break;
                case '%':
                    tokens.push('.*')
                    break;
                default:
                    tokens.push(needle[i]);
                    break;
            }
            ++i;
        }
    }

    return new RegExp(`^${tokens.join('')}$`, `u${ci ? 'i' : ''}`).test(haystack);
}

/**
 * Escapes a string in a way that `strLike` will match it as-is, thus '%' and '_'
 * would match a literal '%' and '_' respectively (and not behave as in a SQL LIKE
 * condition).
 *
 * @param {string} str The string to escape.
 * @returns {string} The escaped string.
 */
function escapeStrLike(str) {
    let tokens = [];

    for (let i = 0; i < str.length; i++) {
        switch (str[i]) {
            case '\\':
                tokens.push('\\\\');
                break;
            case '%':
                tokens.push('\\%')
                break;
            case '_':
                tokens.push('\\_')
                break;
            default:
                tokens.push(str[i]);
        }
    }

    return tokens.join('');
}

The code above is dependant on unorm, and is unicode aware to be able to catch cases like:

strLike('Hello ', 'Hello _'); // true
strLike('Hello ', '_e%o__');  // true
strLike('asdfas \\H\\\\%É\\l\\_\\l\\o asdfasf', '%' . escapeStrLike('\\h\\\\%e\\l\\_\\l\\o') . '%'); // true

Answer 10

I ended up writing a function based on a few answers here that worked pretty well for me. I needed something that would preserve the "startswith%" and "%endswith" syntax, and returns no matches for an empty search string.

function sqlLIKE(target, likeExp) {
  let regex = likeExp
    .replaceAll(/([.*+?^=!:${}()|[\]\/\\])/g, '\\$1')
    .replaceAll("%", ".*")
    .replaceAll("_", ".");

  if (likeExp.charAt(0) !== '%' || !likeExp.includes('%')) regex = `^${regex}`;

  if (likeExp.charAt(likeExp.length - 1) !== '%' || !likeExp.includes('%')) regex = `${regex}$`;

  return new RegExp(regex).exec(target) !== null;
}