Regular Expressions 101

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An explanation of your regex will be automatically generated as you type.
Detailed match information will be displayed here automatically.
  • All Tokens
  • Common Tokens
  • General Tokens
  • Anchors
  • Meta Sequences
  • Quantifiers
  • Group Constructs
  • Character Classes
  • Flags/Modifiers
  • Substitution
  • A single character of: a, b or c
    [abc]
  • A character except: a, b or c
    [^abc]
  • A character in the range: a-z
    [a-z]
  • A character not in the range: a-z
    [^a-z]
  • A character in the range: a-z or A-Z
    [a-zA-Z]
  • Any single character
    .
  • Alternate - match either a or b
    a|b
  • Any whitespace character
    \s
  • Any non-whitespace character
    \S
  • Any digit
    \d
  • Any non-digit
    \D
  • Any word character
    \w
  • Any non-word character
    \W
  • Non-capturing group
    (?:...)
  • Capturing group
    (...)
  • Zero or one of a
    a?
  • Zero or more of a
    a*
  • One or more of a
    a+
  • Exactly 3 of a
    a{3}
  • 3 or more of a
    a{3,}
  • Between 3 and 6 of a
    a{3,6}
  • Start of string
    ^
  • End of string
    $
  • A word boundary
    \b
  • Non-word boundary
    \B

Regular Expression
Processing...

Test String

Code Generator

Generated Code

const regex = / (?: # ---------- (?= (?&V_Obj) ) # Assertion : Must be a Valid JSON Object { | # or , (?! ^ ) # Here we are in a valid JSON Object or Array \G # Continuation anchor, where we last left off (?&Sep_Obj) \s* # Array Separator ) # ---------- (?: (?&V_KeyVal) (?&Sep_Obj) )*? # Drill down to array or string value \s* \K # Stop recording ( (?&Str) ) # (1), The key \s* : \s* (?| # Branch reset \[ # Array values = string, numb, bool, or null ( # (2), Array Contents (?: \s* (?: (?&Numb) # Numbers | (?> true | false | null ) # Boolean and null | (?&Str) # String ) (?&Sep_Ary) # Ary separator )+ ) \s* \] | # Or, ( # (2), A Non-Ary, Non-Obj value (?&Numb) # Numbers | (?> true | false | null ) # Boolean and null | (?&Str) # String ) ) # JSON functions - NoErDet # --------------------------------------------- (?(DEFINE)(?<Sep_Ary>\s*(?:,(?!\s*[}\]])|(?=\])))(?<Sep_Obj>\s*(?:,(?!\s*[}\]])|(?=})))(?<Str>(?>"[^\\"]*(?:\\[\s\S][^\\"]*)*"))(?<Numb>(?>[+-]?(?:\d+(?:\.\d*)?|\.\d+)(?:[eE][+-]?\d+)?|(?:[eE][+-]?\d+)))(?<V_KeyVal>(?>\s*(?&Str)\s*:\s*(?&V_Value)\s*))(?<V_Value>(?>(?&Numb)|(?>true|false|null)|(?&Str)|(?&V_Obj)|(?&V_Ary)))(?<V_Ary>\[(?>\s*(?&V_Value)(?&Sep_Ary))*\s*\])(?<V_Obj>{(?>(?&V_KeyVal)(?&Sep_Obj))*\s*})) /gm; // Alternative syntax using RegExp constructor // const regex = new RegExp(' (?: # ---------- (?= (?&V_Obj) ) # Assertion : Must be a Valid JSON Object { | # or , (?! ^ ) # Here we are in a valid JSON Object or Array \\G # Continuation anchor, where we last left off (?&Sep_Obj) \\s* # Array Separator ) # ---------- (?: (?&V_KeyVal) (?&Sep_Obj) )*? # Drill down to array or string value \\s* \\K # Stop recording ( (?&Str) ) # (1), The key \\s* : \\s* (?| # Branch reset \\[ # Array values = string, numb, bool, or null ( # (2), Array Contents (?: \\s* (?: (?&Numb) # Numbers | (?> true | false | null ) # Boolean and null | (?&Str) # String ) (?&Sep_Ary) # Ary separator )+ ) \\s* \\] | # Or, ( # (2), A Non-Ary, Non-Obj value (?&Numb) # Numbers | (?> true | false | null ) # Boolean and null | (?&Str) # String ) ) # JSON functions - NoErDet # --------------------------------------------- (?(DEFINE)(?<Sep_Ary>\\s*(?:,(?!\\s*[}\\]])|(?=\\])))(?<Sep_Obj>\\s*(?:,(?!\\s*[}\\]])|(?=})))(?<Str>(?>"[^\\\\"]*(?:\\\\[\\s\\S][^\\\\"]*)*"))(?<Numb>(?>[+-]?(?:\\d+(?:\\.\\d*)?|\\.\\d+)(?:[eE][+-]?\\d+)?|(?:[eE][+-]?\\d+)))(?<V_KeyVal>(?>\\s*(?&Str)\\s*:\\s*(?&V_Value)\\s*))(?<V_Value>(?>(?&Numb)|(?>true|false|null)|(?&Str)|(?&V_Obj)|(?&V_Ary)))(?<V_Ary>\\[(?>\\s*(?&V_Value)(?&Sep_Ary))*\\s*\\])(?<V_Obj>{(?>(?&V_KeyVal)(?&Sep_Obj))*\\s*})) ', 'gm') const str = `{ "key1": ["value1","value2","value3","value4","value5",3.14,null], "key_complex_skip": ["valuec", {"subkey": [null,null,34.123] } ], "key2": null, "key3": "value8" } `; // Reset `lastIndex` if this regex is defined globally // regex.lastIndex = 0; let m; while ((m = regex.exec(str)) !== null) { // This is necessary to avoid infinite loops with zero-width matches if (m.index === regex.lastIndex) { regex.lastIndex++; } // The result can be accessed through the `m`-variable. m.forEach((match, groupIndex) => { console.log(`Found match, group ${groupIndex}: ${match}`); }); }

Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions