Determining whether one array contains the contents of another array in JavaScript/CoffeeScript

No set function does this, but you can simply do an ad-hoc array intersection and check the length.

[8, 1, 10, 2, 3, 4, 5, 9].filter(function (elem) {
    return arr1.indexOf(elem) > -1;
}).length == arr1.length

A more efficient way to do this would be to use .every which will short circuit in falsy cases.

arr1.every(elem => arr2.indexOf(elem) > -1);

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