Removes Duplicate JSON Elements for a Value of a Certain Key

JsTips
javascript

This sample removes duplicate JSON elements for a value of a certain key. When the value of the certain key is removed, only a first duplicate element is left. Also I had wanted to be used for Google Apps Script. So it became like this.

Script :

function removeDup(arr, key){
    var temp = [];
    var out = [];
    arr.forEach( function (e, i) {
        temp[i] = (temp.indexOf(e[key]) === -1) ? e[key] : false;
        if (temp[i]) out.push(e);
    });
    return out;
}

JSON :

var arr = [
    {a: "a1", b: "b1", c: "c1"},
    {a: "a2", b: "b1", c: "c1"},
    {a: "a3", b: "b2", c: "c1"},
    {a: "a4", b: "b2", c: "c2"},
    {a: "a5", b: "b3", c: "c2"}
]

Pattern 1:

var key = "b";
var out = removeDup(arr, "key")

[
    { a: 'a1', b: 'b1', c: 'c1' },
    { a: 'a3', b: 'b2', c: 'c1' },
    { a: 'a5', b: 'b3', c: 'c2' }
]

Pattern 2:

var key = "c";
var out = removeDup(arr, "key")

[
    { a: 'a1', b: 'b1', c: 'c1' },
    { a: 'a4', b: 'b2', c: 'c2' }
]

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