Maps and Sets

Set From Array

Remove duplicates, then keep the values that match a rule.

set-from-array `Array.from(new Set(values))` is a compact way to remove duplicates while preserving first-seen order. After that, normal array methods can continue the pipeline.

Set From Array

minLength
set_from_array.js
Replay: real traced execution (multi-file project)
const minLength = 3;
const tags = Array.from(new Set(["js", "web", "js", "trace"]))
  .filter((tag) => tag.length >= minLength)
  .join(",");

console.log("minLength=" + minLength);
console.log("tags=" + tags);

const minLength = 2;
const tags = Array.from(new Set(["js", "web", "js", "trace"]))
  .filter((tag) => tag.length >= minLength)
  .join(",");

console.log("minLength=" + minLength);
console.log("tags=" + tags);

const minLength = 5;
const tags = Array.from(new Set(["js", "web", "js", "trace"]))
  .filter((tag) => tag.length >= minLength)
  .join(",");

console.log("minLength=" + minLength);
console.log("tags=" + tags);

  1. minLength ← 3, tags ← web,trace

    1const minLength→ 3 = 3; //@minLength=2, 52const tags→ web,trace = Array.from(new Set(["js", "web", "js", "trace"]))3  .filter((tag) => tag.length >= minLength)4  .join(",");56console.log("minLength=" + minLength3);7console.log("tags=" + tagsweb,trace);
    outputminLength=3
tags=web,trace

  1. minLength ← 2, tags ← js,web,trace

    1const minLength→ 2 = 2;2const tags→ js,web,trace = Array.from(new Set(["js", "web", "js", "trace"]))3  .filter((tag) => tag.length >= minLength)4  .join(",");56console.log("minLength=" + minLength2);7console.log("tags=" + tagsjs,web,trace);
    outputminLength=2
tags=js,web,trace

  1. minLength ← 5, tags ← trace

    1const minLength→ 5 = 5;2const tags→ trace = Array.from(new Set(["js", "web", "js", "trace"]))3  .filter((tag) => tag.length >= minLength)4  .join(",");56console.log("minLength=" + minLength5);7console.log("tags=" + tagstrace);
    outputminLength=5
tags=trace