Quantifiers of regular series

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Quantifiers indicate the number of characters or expressions to match .

1、x*

Put the previous item “x” matching 0 Times or more .

let reg = /bo*/g;
let str = "A ghost booooed";
str.match(reg); // ['boooo']
str = "A bird warbled";
str.match(reg); // ['b', 'b']
str = "A goat grunted";
str.match(reg); // null

2、x+

Put the previous item “x” matching 1 Times or more , Equivalent to {1,}.

let reg = /bo+/g;
let str = "A ghost booooed";
str.match(reg); // ['boooo']
str = "A bird warbled";
str.match(reg); // null
str = "A goat grunted";
str.match(reg); // null
reg = /a+/g;
str = "caaaaaaandy";
str.match(reg); // ['aaaaaaa']

3、x?

Put the previous item “x” matching 0 or 1 Time .

If in any quantifier *、+、? or {} Then use ?, Then the quantifier is non greedy ( The minimum number of matches ), Not acquiesced greedy ( The maximum number of matches ).

let reg = /bo?/g;
let str = "A ghost booooed";
str.match(reg); // ['bo']
str = "A bird warbled";
str.match(reg); // ['b', 'b']
str = "A goat grunted";
str.match(reg); // null
reg = /bo??/g;
str = "A ghost booooed";
str.match(reg); // ['b']

4、x{n}

among “n” Is a positive integer , With the previous item “x” Of n Secondary match .

let reg = /a{2}/g;
let str = "candy";
str.match(reg); // null
str = "caandy";
str.match(reg); // ['aa']
str = "caaandy";
str.match(reg); // ['aa']

5、x{n,}

among ,“n” Is a positive integer , With the previous item “x” Match at least “n” Time .

let reg = /a{2,}/g;
let str = "caaandy";
str.match(reg); // ['aaa']

6、x{n,m}

among n by 0 Or a positive integer ,m As a positive integer , And m > n, The previous one x Match at least n Times and at most m Time .

let reg = /a{2,4}/g;
let str = "caaaaaaaaaaandy";
str.match(reg); // ['aaaa', 'aaaa', 'aaa']

7、x*?x+?x??x{n}?x{n,}?x{n,m}?

By default , image * and + Such quantifiers are “ Greedy ”, That means they try to match as many strings as possible . The character after the quantifier ? Make quantifier “ Not greed ”： This means that once a match is found , It will stop .

let reg = /a{2,4}?/g;
let str = "caaaaaaaaaaandy";
str.match(reg); // ['aa', 'aa', 'aa', 'aa', 'aa']

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