PHP's json_encode in JavaScript

Here’s what our current JavaScript equivalent to PHP's json_encode looks like. 

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module.exports = function json_encode (mixedVal) { // eslint-disable-line camelcase
  //       discuss at: http://phpjs.org/functions/json_encode/
  //      original by: Public Domain (http://www.json.org/json2.js)
  // reimplemented by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  //      improved by: Michael White
  //         input by: felix
  //      bugfixed by: Brett Zamir (http://brett-zamir.me)
  //        example 1: json_encode('Kevin')
  //        returns 1: '"Kevin"'

  /*
    http://www.JSON.org/json2.js
    2008-11-19
    Public Domain.
    NO WARRANTY EXPRESSED OR IMPLIED. USE AT YOUR OWN RISK.
    See http://www.JSON.org/js.html
  */

  var $global = (typeof window !== 'undefined' ? window : global)
  $global.$locutus = $global.$locutus || {}
  var $locutus = $global.$locutus
  $locutus.php = $locutus.php || {}

  var json = $global.JSON
  var retVal
  try {
    if (typeof json === 'object' && typeof json.stringify === 'function') {
      // Errors will not be caught here if our own equivalent to resource
      retVal = json.stringify(mixedVal)
      if (retVal === undefined) {
        throw new SyntaxError('json_encode')
      }
      return retVal
    }

    var value = mixedVal

    var quote = function (string) {
      var escapeChars = [
        '\u0000-\u001f',
        '\u007f-\u009f',
        '\u00ad',
        '\u0600-\u0604',
        '\u070f',
        '\u17b4',
        '\u17b5',
        '\u200c-\u200f',
        '\u2028-\u202f',
        '\u2060-\u206f',
        '\ufeff',
        '\ufff0-\uffff'
      ].join('')
      var escapable = new RegExp('[\\"' + escapeChars + ']', 'g')
      var meta = {
        // table of character substitutions
        '\b': '\\b',
        '\t': '\\t',
        '\n': '\\n',
        '\f': '\\f',
        '\r': '\\r',
        '"': '\\"',
        '\\': '\\\\'
      }

      escapable.lastIndex = 0
      return escapable.test(string) ? '"' + string.replace(escapable, function (a) {
        var c = meta[a]
        return typeof c === 'string' ? c : '\\u' + ('0000' + a.charCodeAt(0)
          .toString(16))
          .slice(-4)
      }) + '"' : '"' + string + '"'
    }

    var _str = function (key, holder) {
      var gap = ''
      var indent = '    '
      // The loop counter.
      var i = 0
      // The member key.
      var k = ''
      // The member value.
      var v = ''
      var length = 0
      var mind = gap
      var partial = []
      var value = holder[key]

      // If the value has a toJSON method, call it to obtain a replacement value.
      if (value && typeof value === 'object' && typeof value.toJSON === 'function') {
        value = value.toJSON(key)
      }

      // What happens next depends on the value's type.
      switch (typeof value) {
        case 'string':
          return quote(value)

        case 'number':
          // JSON numbers must be finite. Encode non-finite numbers as null.
          return isFinite(value) ? String(value) : 'null'

        case 'boolean':
        case 'null':
          // If the value is a boolean or null, convert it to a string. Note:
          // typeof null does not produce 'null'. The case is included here in
          // the remote chance that this gets fixed someday.
          return String(value)

        case 'object':
          // If the type is 'object', we might be dealing with an object or an array or
          // null.
          // Due to a specification blunder in ECMAScript, typeof null is 'object',
          // so watch out for that case.
          if (!value) {
            return 'null'
          }

          // Make an array to hold the partial results of stringifying this object value.
          gap += indent
          partial = []

          // Is the value an array?
          if (Object.prototype.toString.apply(value) === '[object Array]') {
            // The value is an array. Stringify every element. Use null as a placeholder
            // for non-JSON values.
            length = value.length
            for (i = 0; i < length; i += 1) {
              partial[i] = _str(i, value) || 'null'
            }

            // Join all of the elements together, separated with commas, and wrap them in
            // brackets.
            v = partial.length === 0 ? '[]' : gap
              ? '[\n' + gap + partial.join(',\n' + gap) + '\n' + mind + ']'
              : '[' + partial.join(',') + ']'
            gap = mind
            return v
          }

          // Iterate through all of the keys in the object.
          for (k in value) {
            if (Object.hasOwnProperty.call(value, k)) {
              v = _str(k, value)
              if (v) {
                partial.push(quote(k) + (gap ? ': ' : ':') + v)
              }
            }
          }

          // Join all of the member texts together, separated with commas,
          // and wrap them in braces.
          v = partial.length === 0 ? '{}' : gap
            ? '{\n' + gap + partial.join(',\n' + gap) + '\n' + mind + '}'
            : '{' + partial.join(',') + '}'
          gap = mind
          return v
        case 'undefined':
        case 'function':
        default:
          throw new SyntaxError('json_encode')
      }
    }

    // Make a fake root object containing our value under the key of ''.
    // Return the result of stringifying the value.
    return _str('', {
      '': value
    })
  } catch (err) {
    // @todo: ensure error handling above throws a SyntaxError in all cases where it could
    // (i.e., when the JSON global is not available and there is an error)
    if (!(err instanceof SyntaxError)) {
      throw new Error('Unexpected error type in json_encode()')
    }
    // usable by json_last_error()
    $locutus.php.last_error_json = 4
    return null
  }
}
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How to use

You you can install via npm install locutus and require it via require('locutus/php/json/json_encode'). You could also require the json module in full so that you could access json.json_encode instead.

If you intend to target the browser, you can then use a module bundler such as Browserify, webpack or rollup.js.

ES5/ES6

This function targets ES5, but as of Locutus 2.0.2 we also support ES6 functions. Locutus transpiles to ES5 before publishing to npm.

A community effort

Not unlike Wikipedia, Locutus is an ongoing community effort. Our philosophy follows The McDonald’s Theory. This means that we don't consider it to be a bad thing that many of our functions are first iterations, which may still have their fair share of issues. We hope that these flaws will inspire others to come up with better ideas.

This way of working also means that we don't offer any production guarantees, and recommend to use Locutus inspiration and learning purposes only.

Examples

Please note that these examples are distilled from test cases that automatically verify our functions still work correctly. This could explain some quirky ones.

#codeexpected result
1json_encode('Kevin')'"Kevin"'

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