javascript – find unique objects in array based on multiple properties

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You could build a combined key for the hash table and filter the given array.

var arr = [{ class: "second", fare: "a" }, { class: "second", fare: "b" }, { class: "first", fare: "a" }, { class: "first", fare: "a" }, { class: "second", fare: "a" }, { class: "first", fare: "c" }],
    result = arr.filter(function (a) {
        var key = a.class + '|' + a.fare;
        if (!this[key]) {
            this[key] = true;
            return true;
        }
    }, Object.create(null));

console.log(result);
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The same without (mis)using thisArg of Array#filter.

var array = [{ class: "second", fare: "a" }, { class: "second", fare: "b" }, { class: "first", fare: "a" }, { class: "first", fare: "a" }, { class: "second", fare: "a" }, { class: "first", fare: "c" }],
    seen = Object.create(null),
    result = array.filter(o => {
        var key = ['class', 'fare'].map(k => o[k]).join('|');
        if (!seen[key]) {
            seen[key] = true;
            return true;
        }
    });

console.log(result);
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