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JavaScript Functions Cheat Sheet

Functions and closures

What this cheat sheet is for

This javascript functions reference helps you complete common developer tasks quickly and avoid repeated trial-and-error when working under deadlines.

  • When you need a reliable command or pattern during debugging and incident response.
  • When you are implementing a feature and want a known-good syntax example immediately.
  • When onboarding teammates and documenting repeatable workflows for daily use.
  • When reviewing pull requests and verifying that command usage follows best practices.

Function Declaration

function greet(name) {
  return `Hello ${name}`;
}

Arrow Functions

const greet = (name) => `Hello ${name}`;
const add = (a, b) => a + b;

Closures

function outer() {
  let count = 0;
  return function inner() {
    return ++count;
  };
}

Common mistakes / Pitfalls

  • People often copy a command or pattern without adapting placeholders, which can break production workflows unexpectedly.
  • It is easy to forget environment-specific differences, so always verify behavior in your shell, runtime, or API gateway before shipping.
  • Many errors come from skipping small validation steps, so test with realistic sample input before relying on the result.

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Last updated: February 2026