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Iterate through object properties


Question

var obj = {
    name: "Simon",
    age: "20",
    clothing: {
        style: "simple",
        hipster: false
    }
}

for(var propt in obj){
    console.log(propt + ': ' + obj[propt]);
}

How does the variable propt represent the properties of the object? It's not a built-in method or property. Why does it come up with every property in the object?

2019/03/13
1
2084
3/13/2019 10:58:10 AM


As of JavaScript 1.8.5 you can use Object.keys(obj) to get an Array of properties defined on the object itself (the ones that return true for obj.hasOwnProperty(key)).

Object.keys(obj).forEach(function(key,index) {
    // key: the name of the object key
    // index: the ordinal position of the key within the object 
});

This is better (and more readable) than using a for-in loop.

Its supported on these browsers:

  • Firefox (Gecko): 4 (2.0)
  • Chrome: 5
  • Internet Explorer: 9

See the Mozilla Developer Network Object.keys()'s reference for futher information.

2018/03/30

Girls and guys we are in 2019 and we do not have that much time for typing... So lets do this cool new fancy ECMAScript 2016:

Object.keys(obj).forEach(e => console.log(`key=${e}  value=${obj[e]}`));
2019/10/18

It's the for...in statement (MDN, ECMAScript spec).

You can read it as "FOR every property IN the obj object, assign each property to the PROPT variable in turn".

2014/04/17

In up-to-date implementations of ES, you can use Object.entries:

for (const [key, value] of Object.entries(obj)) { }

or

Object.entries(obj).forEach(([key, value]) => ...)

If you just want to iterate over the values, then use Object.values:

for (const value of Object.values(obj)) { }

or

Object.values(obj).forEach(value => ...)
2019/10/29

It's just a for...in loop. Check out the documentation at Mozilla.

2011/11/29

Source: https://stackoverflow.com/questions/8312459
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