Split keep function. Lookbehind, match, loop

Common code:

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function escapeRegExp(text) {     return text.replace(/[-[\]{}()*+?.,\\^$|#\s]/g, "\\$&"); }

Lookbehind:

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String.prototype.splitKeep = function (tokens) {     const escaped = escapeRegExp(tokens);     return this.split(new RegExp(`(?=[${escaped}])|(?<=[${escaped}])`, "g")); };

Match. Safari does not support lookbehind, use match approach:

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String.prototype.splitKeep = function (tokens) {     const tokensEscaped = tokens         .split("")         .map((s) => escapeRegExp(s))         .join("|");       const wordMatch = `[^${escapeRegExp(tokens)}]+`;     return this.match(new RegExp(tokensEscaped + "|" + wordMatch, "g")); };

Loop-based approach:

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String.prototype.splitKeep = function (tokens) {     let toPush = "";     const splitList = [];     for (const c of this) {         if (tokens.includes(c)) {             if (toPush.length > 0) {                 splitList.push(toPush);             }             splitList.push(c);             toPush = "";             continue;         }           toPush += c;     }       if (toPush.length > 0) {         splitList.push(toPush);     }       return splitList; };

Benchmark code:

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console.time("test"); for (let i = 0; i < 10000; ++i) {     "pin1yin1".splitKeep("12345 "); } console.timeEnd("test");

Results:

% node splitkeep-lookbehind.js
test: 19.35ms
% node splitkeep-lookbehind.js
test: 18.951ms
% node splitkeep-match.js       
test: 54.635ms
% node splitkeep-match.js
test: 51.998ms
% node splitkeep-loop.js 
test: 14.647ms
% node splitkeep-loop.js
test: 13.035ms