Regex that only matches with the given positive number and does not match with the negative number-CodePudding

Sample string: const str = "1 1 2 -2 5 2 4 4 -1 -2 5"

When I do str.match(/1/g) the result is ['1', '1', '1'] which is expected because "... -1 ..." is also getting a match.

The desire is to have a regex str.match(regex) that will only return ['1', '1'].

Ideally the desired regex will be declared like so: let regex = new RegExp(e, "g") where e could be any integer.

CodePudding user response：

Match 1 with a non - before it. Or a beginning of sentence. Thanks to @Lucas Sanchez for the Negative Lookbehind (?<!) Assert that the Regex does not match

const str = "1 1 2 -2 5 2 4 4 -1 -2 5"
var digit = 1;
var reg = new RegExp("(?<!\\S)"   digit   "|^("   digit   ")", "g");
console.log(str.match(reg))

CodePudding user response：

This should do the trick. It uses a negative lookahead and negative lookbehind that looks for non white space characters.

(?<!\S)1(?!\S)

const string = '1 1 2 -2 5 2 4 4 -1 -2 5 1 11 -2 -1';
const regex = /(?<!\S)1(?!\S)/g;
console.log(string.match(regex));

CodePudding user response：

Using javascript string template literals for a more readable code :

const str = "1 1 2 -2 5 2 4 4 -1 -2 5"
const digit = 5;
const reg = new RegExp(`(?<!\\S)${digit}|^(${digit})`, "g");
console.log(str.match(reg))

Output

[LOG]: ["5", "5"]