Determine whether an array contains a value

javascript

array-methods

performance-optimization

best-practices

byAnton Shumikhin·Aug 29, 2024

To check if an array contains a value, utilize array.includes(value) for an immediate boolean result or array.indexOf(value) to obtain the position.

// With includes():
const hasValue = [1, 2, 3].includes(2); // true

// With indexOf():
const index = [1, 2, 3].indexOf(2); // 1

Test for uncertainty or NaN in arrays with some():

const containsNaN = [1, 2, NaN].some(num => Number.isNaN(num)); // true

For browsers with no native includes(), fall back to indexOf() using a polyfill:

if (!Array.prototype.includes) { 
  Array.prototype.includes = function(searchElement, fromIndex) {
    'use strict';
    return this.indexOf(searchElement, fromIndex) !== -1;
  };
}

Dealing with array-like objects

For array-like objects, leverage Array.prototype.includes.call():

function hasElement(element) {
  // "arguments" is array-like; needs special treatment
  return Array.prototype.includes.call(arguments, element);
}

hasElement(1, 2, 3, 4); // true

Writing efficient and maintainable code

Avoid over-reliance on third-party libraries. Instead, use JavaScript's native methods.
Use right-sized lodash imports if you choose lodash. Import only required functions.
Use terse direct application syntax: ["Eat", "Sleep", "Code"].includes("Code") and a friendly alien 👽 will visit you.
Validate your code regularly with online tools like CodePen or JSFiddle.

Advanced array checks and modifications

Multiple value checks

// Checking for acceptance letter from multiple universities
const myUniversities = ['Harvard', 'MIT', 'Princeton'];
const lettersArrived = ['Princeton', 'MIT'];

const gotAnOffer = lettersArrived.every(univ => myUniversities.includes(univ)); // returns true

Performance implications

.includes() can be a performance hog on large data sets. Use with caution and always benchmark when in doubt.

Code readability and maintenance

Use expressive variable names and detailed code comments.
Refer documentation for using techniques and methods aptly, enhancing code quality and readability.

More alternatives in search operations

Use Array.prototype.some() if a matching condition is what you are looking for.
When you need more control, use Array.prototype.filter() to build your search.

Handling issues with cross-browser support

Use polyfills for .includes() from Babel or core-js.
MDN provides a includes() polyfill to ensure your code works on older browsers.
For wider support, consider using lodash's .includes().