In my code, I have a couple of dictionaries (as suggested here) which is String indexed. Due to this being a bit of an improvised type, I was wondering if there any suggestions on how I would be able to loop through each key (or value, all I need the keys for anyway). Any help appreciated!

myDictionary: { [index: string]: any; } = {};

In my code, I have a couple of dictionaries (as suggested here) which is String indexed. Due to this being a bit of an improvised type, I was wondering if there any suggestions on how I would be able to loop through each key (or value, all I need the keys for anyway). Any help appreciated!

myDictionary: { [index: string]: any; } = {};

• javascript
• typescript

Share Improve this question Follow edited Apr 28, 2022 at 9:14 Yves M. 31k2424 gold badges109109 silver badges149149 bronze badges asked Apr 23, 2013 at 16:07 ben657ben657 3,85333 gold badges1818 silver badges1515 bronze badges 3

• 1 Did you try: for (var key in myDictionary) { }? Inside the loop, you'd use key to get the key, and myDictionary[key] to get the value – Ian Commented Apr 23, 2013 at 16:15
• @Ian Just tried that, doesn't seem to be working. No errors, but nothing runs within the statement – ben657 Commented Apr 23, 2013 at 16:21
• 1 @Ian Ah sorry, some code elsewhere was messing with it. That works perfectly! Care to make it an answer so I can choose it? – ben657 Commented Apr 23, 2013 at 16:38

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11 Answers 11

Sorted by: Reset to default 462

To loop over the key/values, use a for in loop:

for (let key in myDictionary) {
    let value = myDictionary[key];
    // Use `key` and `value`
}

< ES 2017:

Object.keys(obj).forEach(key => {
  let value = obj[key];
});

>= ES 2017:

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

How about this?

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

There is one caveat to the key/value loop that Ian mentioned. If it is possible that the Objects may have attributes attached to their Prototype, and when you use the in operator, these attributes will be included. So you will want to make sure that the key is an attribute of your instance, and not of the prototype. Older IEs are known for having indexof(v) show up as a key.

for (const key in myDictionary) {
    if (myDictionary.hasOwnProperty(key)) {
        let value = myDictionary[key];
    }
}

Shortest way to get all dictionary/object values:

Object.keys(dict).map(k => dict[k]);

Or this ways:

Object.entries(dict).map([k,v] => /* ... */);

If you just for in a object without if statement hasOwnProperty then you will get error from linter like:

for (const key in myobj) {
   console.log(key);
}

WARNING in component.ts
for (... in ...) statements must be filtered with an if statement

So the solutions is use Object.keys and of instead.

for (const key of Object.keys(myobj)) {
   console.log(key);
}

Hope this helper some one using a linter.

With es2019, this is now even simpler:

1. We can use of systematic
2. No longer need to wrap the dictionary with Object.entries

Example:

let someMap: Map<number, number> = new Map()
someMap.set(3, 7);
someMap.set(4, 12);
for (let [key, value] of someMap) {
    console.log(key, value)
}

Output:

3 7
4 12

Ians Answer is good, but you should use const instead of let for the key because it never gets updated.

for (const key in myDictionary) {
    let value = myDictionary[key];
    // Use `key` and `value`
}

If you want to loop only through object value take a look at Object.values

To get the keys:

function GetDictionaryKeysAsArray(dict: {[key: string]: string;}): string[] {
  let result: string[] = [];
  Object.keys(dict).map((key) =>
    result.push(key),
  );
  return result;
}

this is my function, i hope this help

function recordToArray<TypeOfSchema>(
  data: Record<string, TypeOfSchema>
): Array<TypeOfSchema> {
  return Object.keys(data).map((key: string) => ({ id: key, ...data[key] }));
}