Javascript entry（）不返回任何内容

Question

I want to get the array elements, with their indexes, I use entries() as below but it does not print out anything, and it does not give any errors.

 var array1 = ['a', 'b', 'c']; var iterator1 = array1.entries(); for ([k, v] in iterator1) { console.log(k, v) } 

Answer 1

You should use for of instead of for in

 var array1 = ['a', 'b', 'c']; var iterator1 = array1.entries(); for ([k, v] of iterator1) { console.log(k, v) } 

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Another way is to use done property and next method of iterators

 var array1 = ['a', 'b', 'c']; var iterator1 = array1.entries(); let result = iterator1.next() while (!result.done) { let [k, v] = result.value console.log(k, v) result = iterator1.next() } 

Answer 2

To use index and element of an array, you can use the const [key, value] notation in conjunction with the of keyword, in order to use the iterator.

 const a = ['a', 'b', 'c']; for (const [index, element] of a.entries()) { console.log(index, element); } // 0 'a' // 1 'b' // 2 'c' 

You could also call next on the iterator directly.

 var array1 = ['a', 'b', 'c']; var iterator1 = array1.entries(); console.log(iterator1.next().value); // expected output: Array [0, "a"] console.log(iterator1.next().value); // expected output: Array [1, "b"] 

See also: Mozilla docs - Array.entries()