Как найти элементы массива в другом массиве

If you don’t need type coercion (because of the use of indexOf), you could try something like the following:

var arr = [1, 2, 3];
var check = [3, 4];

var found = false;
for (var i = 0; i < check.length; i++) {
    if (arr.indexOf(check[i]) > -1) {
        found = true;
        break;
    }
}
console.log(found);

Where arr contains the target items. At the end, found will show if the second array had at least one match against the target.

Of course, you can swap out numbers for anything you want to use — strings are fine, like your example.

And in my specific example, the result should be true because the second array’s 3 exists in the target.

UPDATE:

Here’s how I’d organize it into a function (with some minor changes from before):

var anyMatchInArray = (function () {
    "use strict";

    var targetArray, func;

    targetArray = ["apple", "banana", "orange"];
    func = function (checkerArray) {
        var found = false;
        for (var i = 0, j = checkerArray.length; !found && i < j; i++) {
            if (targetArray.indexOf(checkerArray[i]) > -1) {
                found = true;
            }
        }
        return found;
    };

    return func;
}());

DEMO: http://jsfiddle.net/u8Bzt/

In this case, the function could be modified to have targetArray be passed in as an argument instead of hardcoded in the closure.

UPDATE2:

While my solution above may work and be (hopefully more) readable, I believe the «better» way to handle the concept I described is to do something a little differently. The «problem» with the above solution is that the indexOf inside the loop causes the target array to be looped over completely for every item in the other array. This can easily be «fixed» by using a «lookup» (a map…a JavaScript object literal). This allows two simple loops, over each array. Here’s an example:

var anyMatchInArray = function (target, toMatch) {
    "use strict";

    var found, targetMap, i, j, cur;

    found = false;
    targetMap = {};

    // Put all values in the `target` array into a map, where
    //  the keys are the values from the array
    for (i = 0, j = target.length; i < j; i++) {
        cur = target[i];
        targetMap[cur] = true;
    }

    // Loop over all items in the `toMatch` array and see if any of
    //  their values are in the map from before
    for (i = 0, j = toMatch.length; !found && (i < j); i++) {
        cur = toMatch[i];
        found = !!targetMap[cur];
        // If found, `targetMap[cur]` will return true, otherwise it
        //  will return `undefined`...that's what the `!!` is for
    }

    return found;
};

DEMO: http://jsfiddle.net/5Lv9v/

The downside to this solution is that only numbers and strings (and booleans) can be used (correctly), because the values are (implicitly) converted to strings and set as the keys to the lookup map. This isn’t exactly good/possible/easily done for non-literal values.

Here’s a way I am doing it after researching it for a while. I wanted to make a Laravel API endpoint that checks if a field is «in use», so the important information is: 1) which DB table? 2) what DB column? and 3) is there a value in that column that matches the search terms?

Knowing this, we can construct our associative array:

$SEARCHABLE_TABLE_COLUMNS = [
    'users' => [ 'email' ],
];

Then, we can set our values that we will check:

$table = 'users';
$column = 'email';
$value = 'alice@bob.com';

Then, we can use array_key_exists() and in_array() with eachother to execute a one, two step combo and then act upon the truthy condition:

// step 1: check if 'users' exists as a key in `$SEARCHABLE_TABLE_COLUMNS`
if (array_key_exists($table, $SEARCHABLE_TABLE_COLUMNS)) {

    // step 2: check if 'email' is in the array: $SEARCHABLE_TABLE_COLUMNS[$table]
    if (in_array($column, $SEARCHABLE_TABLE_COLUMNS[$table])) {

        // if table and column are allowed, return Boolean if value already exists
        // this will either return the first matching record or null
        $exists = DB::table($table)->where($column, '=', $value)->first();

        if ($exists) return response()->json([ 'in_use' => true ], 200);
        return response()->json([ 'in_use' => false ], 200);
    }

    // if $column isn't in $SEARCHABLE_TABLE_COLUMNS[$table],
    // then we need to tell the user we can't proceed with their request
    return response()->json([ 'error' => 'Illegal column name: '.$column ], 400);
}

// if $table isn't a key in $SEARCHABLE_TABLE_COLUMNS,
// then we need to tell the user we can't proceed with their request
return response()->json([ 'error' => 'Illegal table name: '.$table ], 400);

I apologize for the Laravel-specific PHP code, but I will leave it because I think you can read it as pseudo-code. The important part is the two if statements that are executed synchronously.

array_key_exists() and in_array() are PHP functions.

source:

• https://php.net/manual/en/function.array-key-exists.php

• https://php.net/manual/en/function.in-array.php

The nice thing about the algorithm that I showed above is that you can make a REST endpoint such as GET /in-use/{table}/{column}/{value} (where table, column, and value are variables).

You could have:

$SEARCHABLE_TABLE_COLUMNS = [
    'accounts' => [ 'account_name', 'phone', 'business_email' ],
    'users' => [ 'email' ],
];

and then you could make GET requests such as:

GET /in-use/accounts/account_name/Bob's Drywall (you may need to uri encode the last part, but usually not)

GET /in-use/accounts/phone/888-555-1337

GET /in-use/users/email/alice@bob.com

Notice also that no one can do:

GET /in-use/users/password/dogmeat1337 because password is not listed in your list of allowed columns for user.

Good luck on your journey.

Если @egor_nullptr вас понял правильно, и вам нужно проверить, что массив b хотя бы в одном экзепляре содержит каждый элемент массива a, то предлагаю такое решение:

Array.prototype.hasAll = function(a) {
    var hash = this.reduce(function(acc, i) { acc[i] = true; return acc; }, {});
    return a.every(function(i) { return i in hash; });
};

По сравнению с решением @egor_nullptr оно асимптотически быстрее: O(n + m) против O(n * m), где n, m — размеры массивов a, b. При n = m = 100 000 на моей машине мой вариант отрабатывает быстрее в 200 раз. Тестировал так.

Знаете, каков мой опыт разработки на JavaScript? Я программирую на нём 40 минут, в обнимку с JavaScript Reference от Mozilla. Мой основной язык — C++. А вам очень советую добраться-таки до какой-нибудь книжки по алгоритмам и структурам данных (например, до «Introduction to Algorithms». Она есть на русском, лучший перевод, на мой взгляд, от МЦНМО). Это полезно, уверяю вас.