# Reference Guide

A quick reference for commonly used JavaScript methods and browser APIs.

Unless otherwise noted, these work in all modern browsers on desktop and mobile. You can extend support back further with polyfills.

## Numbers

• parseInt() - Convert a string into an integer (whole number).
• parseFloat() - Convert a string into a point number (a number with decimal points).
• Number() - Convert a string into a number.
• Number.toFixed() - Format a number to a fixed number of decimal places.
• Number.toString() - Convert a number to a string.
• Basic math - Do basic arithmetic with JavaScript.
• Comparisons - Compare two numbers.
• Math.abs() - Get the absolute value of a number.
• Math.floor() - Get the largest integer less than or equal to a number.
• Math.ceil() - Get the smallest integer greater than or equal to a number.
• Math.max() - Get the largest number from a set of numbers
• Math.min() - Get the lowest number from a set of numbers.
• Math.random() - Return a random float between `0` and `1`.

## Arrays

• Array.push() - Add items to an array.
• Array.concat() - Merge two or more arrays together.
• Array.slice() - Copy a segment of an array into a new array.
• Array.splice() - Delete, replace, and add items to an array at specific indexes.
• Array.from() - Create a new array from an existing array or array-like object.
• Array.map() - Transform the items in an array and create a new one.
• Array.filter() - Create a new array containing a subset of items from an existing ones.
• Array.reduce() - Take the content of an array and return a single value.
• Array.reverse() - Reverse the order of items in an array.
• Array.join() - Combine all items in an array into a string.
• Array.indexOf() - Get the index of the first matching item in an array.

## Distances

• window.pageYOffset - Get the distance a user has scrolled from the top of the page.
• getOffsetTop() - Get an element’s distance from the top of the document.