Modern browsers have Array#includes, which does exactly that and is widely supported by everyone except IE:

console.log(['joe', 'jane', 'mary'].includes('jane')); //true

You can also use Array#indexOf, which is less direct, but doesn’t require polyfills for outdated browsers.

console.log(['joe', 'jane', 'mary'].indexOf('jane') >= 0); //true

Many frameworks also offer similar methods:

  • jQuery: $.inArray(value, array, [fromIndex])
  • Underscore.js: _.contains(array, value) (also aliased as _.include and _.includes)
  • Dojo Toolkit: dojo.indexOf(array, value, [fromIndex, findLast])
  • Prototype: array.indexOf(value)
  • MooTools: array.indexOf(value)
  • MochiKit: findValue(array, value)
  • MS Ajax: array.indexOf(value)
  • Ext: Ext.Array.contains(array, value)
  • Lodash: _.includes(array, value, [from]) (is _.contains prior 4.0.0)
  • Ramda: R.includes(value, array)

Notice that some frameworks implement this as a function, while others add the function to the array prototype.