检查来自不同数组的两个元素的一个属性是否相等？

Question

At present I've been using nested for loops to solve this issue:

for (var i = 0; i < this.props.trackedPlayers.length; i++)
{
    for (var j = 0; j < PHP_VARS.players_data.length; j++)
    {
        // This check here is the key part
        if (PHP_VARS.players_data[j]._id == this.props.trackedPlayers[i]._id)
        {
            data.push(// stuff from both arrays..);
        }
    }
}

However I figured there might be a boilerplate function that does this already. Done a few searches but nothing cropped up - any pointers, or is this the best I've got for now?

EDIT: Brief explanation, trackedPlayers are all from players_data. By checking if each player in the (generally) larger players_data is in trackedPlayers, I know whether or not to list them as an option for 'adding' to an HTML select field.

Answer 1

You could use an object as hash table and iterate over both arrays, first for the building of the hash table and the second for test and further operations.

var object = Object.create(null);
this.props.trackedPlayers.forEach(function (a) {
    object[a._id] = a;
});
PHP_VARS.players_data.forEach(function (a) {
    if (object[a._id]) {
        // access data from this.props.trackedPlayers
        // with object[a._id]._id as example
        // access data from  PHP_VARS.players_data
        // with a._id as example
        data.push(/* stuff from both arrays..*/);
    }
});

Answer 2

lodash library has _.intersectionBy() function which does exactly what you want. Using this, you could change your code to that:

_.intersectionBy([PHP_VARS.players_data, this.props.trackedPlayers], "_id")
  .forEach(element=> {
    data.push(/* ... */)
  })

or, using for...of loop:

const intersection = _.intersectionBy([PHP_VARS.players_data, this.props.trackedPlayers], "_id")
for (element of intersection) {
  data.push(/* ... */)
}