You can traverse the properties or values of JavaScript objects through various methods, because the object itself cannot be iterated directly with for...of. 1. Use the for...in loop combined with hasOwnProperty() to traverse its own enumerable property keys; 2. Use Object.keys() to iterate over the keys of the object itself; 3. Use Object.values() to traverse for...of to iterate over the values of all its enumerable properties; 4. Use Object.entries() to combo for...of or forEach() to get key-value pairs at the same time; 5. Use Object.getOwnPropertyNames() to contain non-enumerable property names, but do not include Symbol properties. It is recommended to select methods according to your needs, and pay attention to distinguishing between itself and inherited properties.
You can't directly iterate over an object in JavaScript using standard loop constructs like for...of , because objects are not iterable by default. However, there are several ways to loop through an object's properties or values, depending on what you need.
Here are the most common and effective methods:
1. for...in loop (Iterate over keys)
The for...in loop goes through all enumerable string properties of an object, including inherited ones (from the prototype chain), so it's important to use hasOwnProperty() to filter out inherited properties.
const obj = { a: 1, b: 2, c: 3 };
for (let key in obj) {
if (obj.hasOwnProperty(key)) {
console.log(key, obj[key]);
}
}
// Output:
// a 1
// b 2
// c 3This is the most traditional way and works in older environments.
2. Object.keys() for...of (Iterate over keys)
Object.keys() returns an array of an object's own enumerable property names (keys), which you can then iterate over.
const obj = { a: 1, b: 2, c: 3 };
for (let key of Object.keys(obj)) {
console.log(key, obj[key]);
}
// Output:
// a 1
// b 2
// c 3This is clean and modern, and allows you to use array methods if needed.
3. Object.values() for...of (Iterate over values)
If you only care about the values, use Object.values() .
const obj = { a: 1, b: 2, c: 3 };
for (let value of Object.values(obj)) {
console.log(value);
}
// Output:
// 1
// 2
// 3 4. Object.entries() for...of (Iterate over key-value pairs)
Use Object.entries() to get an array of [key, value] pairs. This is especially useful when you need both key and value.
const obj = { a: 1, b: 2, c: 3 };
for (let [key, value] of Object.entries(obj)) {
console.log(key, value);
}
// Output:
// a 1
// b 2
// c 3 You can also use this with .forEach() :
Object.entries(obj).forEach(([key, value]) => {
console.log(key, value);
}); 5. Using Object.getOwnPropertyNames()
Similar to Object.keys() , but include non-enumerable properties (except symbols).
for (let key of Object.getOwnPropertyNames(obj)) {
console.log(key, obj[key]);
}Useful if you need to include non-enumerable own properties.
Important Notes:
- Symbols : None of the above methods (except
Object.getOwnPropertySymbols()) include properties with symbol keys. - Prototype properties : Always prefer
hasOwnProperty()withfor...in, or useObject.keys()/entries()which only includes own properties. - Order : Since ES2015, the order of properties is predictable: keys appear in the order they were added, for string keys that aren't integers.
In short, for most use cases:
- Use
for...inwithhasOwnProperty()for broad compatibility. - Use
Object.keys(),Object.values(), orObject.entries()withfor...ofor array methods for cleaner, modern code.
Basically, pick the method based on whether you need keys, values, or both — and whether you want only own properties.
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