有没有一种方法可以用一个重复的元素替换单个数组元素？

Question

I'm trying to replace the elements of an array with 1 element repeated for each index.

Eg ['12','a','drink','cookie'] becomes ['0','0','0','0']

I'm learning basic JavaScript and trying to figure out how to do this. I've tried forEach() and splice() but I keep ending up with just one index (eg ['0'] ). I feel like I can solve this with a for loop but what to put in? The code below is my latest effort but it didn't run.

function replace()
{
    var Word = 'test';
    var newWordArray = Array.from(Word);

    for (var i = 0; i < newWordArray.length; i++); {
        i = '0';
    }
}

I expect ['0','0','0','0'] as output, but I get undefined when trying to run the function.

Answer 1

You have a couple of issues with your code:

1. i = '0' isn't doing what you think it is doing. Here i is just a number, representing an index in your array. Changing i will do nothing as you're not doing anything with the value of i itself. Instead your need to change the element at index i . You can do this by doing newWordArray[i] = 0 . This way you are saying change the element at index i in your array newWordArray .

2. You are not returning anything from your function. In order for your function to get assigned a value once called, you need to return said value. Thus, as you want your function call to output (return) a new array, you need to return newWordArray at the end of your function.

3. Although it isn't necessary, I suggest that you add a parameter to your function called word . This way the function can accept a string (or array) and give you the required output.

See working example below:

 function replace(word) { // accept a word as an input to use in your function var newWordArray = Array.from(word); // create an array of characters from your inputted word for (var i = 0; i < newWordArray.length; i++) { // remove ';' colon here newWordArray[i] = 0; // Set every element (by accessing it using its index 'i') to 0 } return newWordArray; // output (return) the new array } console.log(replace("test")); // input "test" as the word variable console.log(replace(['12','a','drink','cookie'])); 

Also note Array.from([1, 2, 3]) will give an array in return, so [1, 2, 3] . Thus the above works on both strings and arrays.

Alternatively, a different approach to achieving the same thing as above would be to use Array.prototype.fill() . Here I have used ES6 arrow functions with destructing assignment :

 const replace = ({length}) => Array(length).fill(0); console.log(replace("testing")); console.log(replace(['12','a','drink','cookie'])); 

Answer 2

Nick Parsons , already explained so good how to change your code to approach your goal, however, and since you are already using Array::from() , you can use the mapFn argument and reduce your code to be more simple, like this:

 const replace = (word, replaceVal) => Array.from(word, x => replaceVal); console.log(replace("word", 0)); console.log(replace("Hello World", 5)); 

Answer 3

You just have to assign it to each element in the array:

for (var i = 0; i < newWordArray.length; i++); {
    newWordArray[i] = '0';
}

You were assigning the value to the iterator.

Answer 4

Here array map shortens your code

 var Word = 'test'; //var newWordArray = Array.from(Word); let j=Array.from(Word).map(a=>a='0'); console.log(j) 

Answer 5

I prefer splice and forEach to achieve this

var contents = ['a','b','c','d'];
document.getElementById('LW').value = contents 

contents.forEach(function(element, index) {
    contents.splice(index, 1, "0");
});