TS · performance

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no-string-concat-in-loop

Prefer collecting string fragments over repeatedly accumulating a growing string inside a loop.

noStringConcatInLoopnoStringReduce Rule source Tests Catalog JSON

Why

Repeatedly rebuilding a growing string can copy all prior content on each iteration, making total work grow quadratically.

Fix

Consider collecting fragments and joining once; preserve intermediate observations and coercion timing, and measure hot paths.

Examples

Before — flagged Do not rebuild a growing string in a loop

src/render.ts

let output = "";
for (const item of items) {
  output = `${output}${item}`;
}

After — preferred Join collected fragments after the loop

src/render.ts

const parts = [];
for (const item of items) {
  parts.push(item);
}
const output = parts.join("");