javascript higher order function variable undefined

Question

I have this array of objects and want the unique elements given a specific key. The array looks like this:

var items = [
    {name: "item1", year : 2013, value : 100},
    {name: "item1", year : 2012, value : 97},
    {name: "item3", year : 2013, value : 93 },
    {name: "item3", year : 2012, value : 91 },
    {name: "item2", year : 2012, value : -6 },
    {name: "item2", year : 2011, value : -5 },
    {name: "item4", year : 2012, value : -36 },
    {name: "item3", year : 2011, value : 93 },
    {name: "item4", year : 2013, value : -35 },
    {name: "item1", year : 2011, value : 98},
    {name: "item2", year : 2013, value : -7 },
    {name: "item4", year : 2011, value : -37 },
    {name: "item5", year : 2013, value : 58 },
    {name: "item5", year : 2012, value : 55 },
    {name: "item5", year : 2011, value : 54 }];

I get the list of unique elements for the key name with the following function:

var unique = function (arr) {
    return arr.reduce(function (prev, curr) {
        if (prev.indexOf(curr.name) === -1) {prev.push(curr.name)}
        return prev;
    }, [])}

so when I do console.log(unique(items)) I get the correct array:

[ 'item1', 'item3', 'item2', 'item4', 'item5' ]

If I change name with year in curr.name i get the correct result. I want to do a higher order function so I can both pass the array I am working on and the key, so I would do unique(items, 'name') or alternatively unique(items, 'year') however when I transform my unique function to this:

var unique = function (arr, criteria) {
    return arr.reduce(function (prev, curr) {
        if (prev.indexOf(curr.criteria) === -1) {prev.push(curr.criteria)}
        return prev;
    }, [])}

and I do console.log(unique(items, 'name')) I get undefined!? and if I do console.log(unique(items, name) I get an error ReferenceError: name is not defined !!

Denys Séguret · Accepted Answer · 2014-09-05 07:41:49Z

2

Use the bracket notation to access the property :

if (prev.indexOf(curr[criteria]) === -1) {prev.push(curr[criteria])}

answered Sep 5, 2014 at 7:41

Denys Séguret

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