内容简介:Since every item in the array is less than 10, the
Array.every()
and Array.some()
are handy JavaScript array methods that can help you test an array against specified criteria. In this post, we’ll quickly learn how to use them.
Array.every()
Array.every
takes a callback function
as an argument. If the function returns true
for each item in the array, Array.every
returns true. Let’s check it out.
function test(el) {
return el < 10;
}
[1, 2, 3, 4, 5, 6].every(test);
// true
Since every item in the array is less than 10, the Array.every
method returns true
.
It’s common to pass an anonymous arrow function directly to the every
method, so let’s do that to see a more familiar syntax:
[1, 2, 3, 4, 5, 6].every(el => el < 10);
// true
Let’s see another example. This time it’ll fail because not every element will pass the test.
[1, 2, 3, 4, 5, 6].every(el => el < 5);
// false
One nice thing that happens here is that, not only does it fail, but it exits early as soon as an element fails the test. That means it won’t even run the test on the last element of the array.
Array.some()
The Array.some
method tests to see if at least one
element of an array passes the test. This time, we’ll start with a failing example:
[1, 2, 3, 4, 5, 6].some(el => el > 10);
// false
Since none of the elements are greater than 10, Array.some
returns false
after testing each element.
Now a scenario that returns true
:
[1, 2, 3, 4, 5, 6].some(el => el > 3);
// true
Not only does it return true
, it returns true as soon as the first element passes the test
. In this cases, since the number 4
passes the test, 5
and 6
aren’t even tested.
Other Functionality
Now that we generally know how the every
and some
methods work, here are some additional functionality you can get out of them:
-
The
Array.everyandArray.somecan take a second argument that will be used asthisin the execution of the callback function. - The callback function can take two additional arguments: the current item’s index and a reference to the array upon which the method was called.
Let’s cram all these additional features into an example:
const obj = { name: 'Daffodil' };
[1, 2, 3, 4, 5, 6].every(function(el, i, arr) {
return el > i && arr[i] === el && this === obj;
}, obj);
// true
So why is this true?
- Each element is greater than its index
-
arr[i](whereiis the current index` is identical to the current element) -
Since we provided a reference to
objas thethisargument,thisis equal toobj
Conclusion
Hopefully you now have a couple additional array methods in your arsenal. Happy coding!
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