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JavaScript cheat sheet

Modern JavaScript you write every day, with short examples. Click one to copy it.

Variables and basics

: Value that won’t be reassigned (use by default)
: Value that will change
: Arrow function with a template string
: Equal, without type conversion (!== for not equal)
: Short if/else
: "string", "number", "object", "undefined"…

Arrays

: New array with each item changed
: New array with the items that pass
: Combine everything into one value
: First match, or undefined (findIndex for its position)
: Is at least one true? (every: are all?)
: Is this value in the array?
: Do something with each item
: Add to the end (pop removes the last)
: First 3 items, without changing the array
: Sorted copy, numbers small to large
: Sorted copy by name (newer browsers)
: Array to text
: Remove duplicates
: Last item
: [0, 1, 2, 3, 4]

Strings

: Remove spaces at both ends
: lowercase (toUpperCase for CAPITALS)
: Contains? (startsWith, endsWith too)
: Text to array
: Replace every match
: First 10 characters
: "7" → "07"
: Text to number (NaN if it isn’t one)
: Number to text with 2 decimals
: 1234567 → "1,234,567"

Objects

: Destructuring: take properties into variables
: Destructure an array
: Copy an object and change a property
: Property names (values, entries too)
: Loop over keys and values
: Optional chaining: undefined instead of an error
: Fallback only for null or undefined
: Deep copy
: Object to JSON text (JSON.parse back)

Async

: Get JSON from an API
: Send JSON
: Handle errors
: Run several at once and wait for all
: Wait one second
: Run once later (setInterval: repeat)

The page (DOM)

: First element matching a CSS selector
: All matching elements
: React to a click
: Change the text
: Add or remove a class (add, remove too)
: Read data-id="…"
: Remember a value in this browser

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