TypeScript, Looping through a dictionary
JavascriptTypescriptJavascript Problem Overview
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 Solutions
Solution 1 - Javascript
To loop over the key/values, use a for in
loop:
for (let key in myDictionary) {
let value = myDictionary[key];
// Use `key` and `value`
}
Solution 2 - Javascript
< ES 2017:
Object.keys(obj).forEach(key => {
let value = obj[key];
});
>= ES 2017:
Object.entries(obj).forEach(
([key, value]) => console.log(key, value)
);
Solution 3 - Javascript
How about this?
for (let [key, value] of Object.entries(obj)) {
...
}
Solution 4 - Javascript
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];
}
}
Solution 5 - Javascript
Shortest way to get all dictionary/object values:
Object.keys(dict).map(k => dict[k]);
Or this ways:
Object.entries(dict).map([k,v] => /* ... */);
Solution 6 - Javascript
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.
Solution 7 - Javascript
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`
}
Solution 8 - Javascript
With es2019, this is now even simpler:
- We can use
of
systematic - 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
Solution 9 - Javascript
To get the keys:
function GetDictionaryKeysAsArray(dict: {[key: string]: string;}): string[] {
let result: string[] = [];
Object.keys(dict).map((key) =>
result.push(key),
);
return result;
}
Solution 10 - Javascript
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] }));
}