JavaScript String Methods Cheat Sheet: Slice, Split, Replace & Template Literals

JavaScript strings are immutable UTF-16 sequences. Methods like slice, split, trim, and replaceAll return new strings. Template literals interpolate values and multi-line text. Do not use length as a character count when emoji or combining marks matter — use Intl.Segmenter or [...str].

This JavaScript cheat sheet is written for people searching for a fast, accurate reference: students, junior developers, and teams shipping production software. Pin it, copy the snippets, and come back when syntax slips.

Quick reference

• slice: str.slice(0, 8) copy. Negative indexes count from the end.
• split / join: csv.split(",") and parts.join(" · ").
• trim: trim, trimStart, trimEnd for form input.
• search: includes, startsWith, endsWith — case-sensitive. Normalize with toLowerCase.
• replace: replace changes one match unless you pass /g. replaceAll needs a string or global regex.
• pad: padStart(2, "0") for clocks and invoice numbers.
• template: ` Hello ${name} `. Escape user HTML before inserting into the DOM.
• Number: Number.parseInt(str, 10) and Number(str) — watch empty string → 0.

Copy-paste examples

Slug and display helpers

Normalize once, then compare. replaceAll is clearer than /g for literal separators.

function slugify(title) {
  return title
    .trim()
    .toLowerCase()
    .replaceAll(' ', '-')
    .replaceAll(/[^a-z0-9-]/g, '');
}
function initials(name) {
  return name
    .trim()
    .split(/\s+/)
    .map((p) => p[0])
    .join('')
    .toUpperCase();
}

Common mistakes

• Mutating thinking: str.replace does nothing unless you assign the return value.
• parseInt("08") without radix in old engines; always pass 10.
• Building HTML with template literals from user input (XSS).
• Using split("") on emoji strings and breaking characters.

FAQ

1. String vs String object? Prefer primitives "hi". new String() boxes and fails some === checks. You almost never need the constructor.

1. BLOGPH0 for strings? Use ===. Coercion with numbers ("10" == 10) hides bugs.

1. How do I pad a month? String(month).padStart(2, "0") → "09".

Related JavaScript cheat sheets

• Javascript Cheat Sheet 2026
• Javascript Array Methods Cheat Sheet
• Javascript Dom Cheat Sheet

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