Write a JavaScript function to get the first element of an array. Passing a parameter 'n' will return the first 'n' elements of the array. ES6 Version: var first = (array, n) => { if (array == null) return void 0; if (n == null) return array[0]; if (n < 0) return []; return array.
To find the index of an object in an array, by a specific property: Use the map() method to iterate over the array, returning only the value of the relevant property. Call the indexOf() method on the returned from map array. The indexOf method returns the index of the first occurrence of a value in an array.
The filter() method is used to filters all the elements and returns the element that matches and the element that do not match are removed. The only difference is the filter() method search through all the elements while find() method search through all the child elements only.
Return Value: It returns a new array and elements of arrays are result of callback function. Below examples illustrate the use of array map() method in JavaScript: Example 1: This example use array map() method and return the square of array element.
Since ES6 there is the native find
method for arrays; this stops enumerating the array once it finds the first match and returns the value.
const result = someArray.find(isNotNullNorUndefined);
Old answer:
I have to post an answer to stop these filter
suggestions :-)
since there are so many functional-style array methods in ECMAScript, perhaps there's something out there already like this?
You can use the some
Array method to iterate the array until a condition is met (and then stop). Unfortunately it will only return whether the condition was met once, not by which element (or at what index) it was met. So we have to amend it a little:
function find(arr, test, ctx) {
var result = null;
arr.some(function(el, i) {
return test.call(ctx, el, i, arr) ? ((result = el), true) : false;
});
return result;
}
var result = find(someArray, isNotNullNorUndefined);
As of ECMAScript 6, you can use Array.prototype.find
for this. This is implemented and working in Firefox (25.0), Chrome (45.0), Edge (12), and Safari (7.1), but not in Internet Explorer or a bunch of other old or uncommon platforms.
For example, x
below is 106
:
const x = [100,101,102,103,104,105,106,107,108,109].find(function (el) {
return el > 105;
});
console.log(x);
If you want to use this right now but need support for IE or other unsupporting browsers, you can use a shim. I recommend the es6-shim. MDN also offers a shim if for some reason you don't want to put the whole es6-shim into your project. For maximum compatibility you want the es6-shim, because unlike the MDN version it detects buggy native implementations of find
and overwrites them (see the comment that begins "Work around bugs in Array#find and Array#findIndex" and the lines immediately following it).
What about using filter and getting the first index from the resulting array?
var result = someArray.filter(isNotNullNorUndefined)[0];
ES6
find()
find()
is located on Array.prototype
so it can be used on every array.find()
takes a callback where a boolean
condition is tested. The function returns the value (not the index!)const array = [4, 33, 8, 56, 23];
const found = array.find(element => {
return element > 50;
});
console.log(found); // 56
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