Array .filter() / find() / findIndex()

// Extracts all elements that match the condition.
var result = array.filter(function(element, index, array) {
	return condition;
});

// Returns the first element that matches the condition.
var item = array.find(function(element, index, array) {
	return condition;
});

// Returns the index of the first element that matches the condition.
var index = array.findIndex(function(element, index, array) {
	return condition;
});

sample_filter.js

var scores = [45, 82, 70, 95, 60, 38];

// Extracts all scores of 70 or above.
var passed = scores.filter(function(score) {
	return score >= 70;
});
console.log(passed); // Outputs '82,70,95'.

// Returns the first score of 80 or above.
var first = scores.find(function(score) {
	return score >= 80;
});
console.log(first); // Outputs '82'.

// Returns the index of the first score of 80 or above.
var index = scores.findIndex(function(score) {
	return score >= 80;
});
console.log(index); // Outputs '1'.

// Searches an array of objects.
var users = [
	{ name: "Okabe Rintaro", age: 18, org: "Future Gadget Lab" },
	{ name: "Makise Kurisu", age: 18, org: "Future Gadget Lab" },
	{ name: "Shiina Mayuri", age: 16, org: "Future Gadget Lab" }
];
var user = users.find(function(u) {
	return u.name === "Makise Kurisu";
});
console.log(user.age); // Outputs '18'.

[ 82, 70, 95 ]
82
1
18

array.filter() runs a callback function on each element of the array and creates a new array containing only the elements for which the callback returns true. The original array is not modified. If no elements match the condition, an empty array is returned, so you can safely loop over the result without additional checks.

array.find() returns only the first element that matches the condition, making it useful for looking up a specific item in an array of objects. If no match is found, it returns undefined, so always check the result before using it when the element may not exist. array.findIndex() works the same way but returns the index of the element rather than the element itself.

If you only need to check whether a value exists in an array, use array.includes(). To check whether all or some elements satisfy a condition, use array.some() / array.every().