如何从对象中删除数组值

Question

var obj = {
a: [1, 3, 4],
b: 2,
c: ['hi', 'there']
   }
   removeArrayValues(obj);
   console.log(obj); // --> { b: 2 }

Here is my code:

function removeArrayValues(obj) {
 for (var key in obj){
 if (Array.isArray(obj[key])) delete obj[key]
 //return obj[key] -> {b: 2, c: ["hi", "there"]}
 }
 return obj[key]
}

Why does it return only obj["a"] and obj["c"] when I return it inside the for/in loop and not obj["k"] . I figured the problem out right before I was about to post this but I run into this issue a lot with both arrays and objects and could use an explanation of what is going on here.

Answer 1

First, let's see your object. It has 3 key/value pairs:

var obj = {
    a: [1, 3, 4],//the value here is an array
    b: 2,//the value here is not an array
    c: ['hi', 'there']//the value here is an array
};

For each key in that object, your removeArrayValues function will delete any of them which has an array as value:

if (Array.isArray(obj[key]))

That condition will return "true" if the value is an array. You can check this in this demo: the console.log inside the for loop will log "true", "false" and "true":

 var obj = { a: [1, 3, 4], b: 2, c: ['hi', 'there'] } removeArrayValues(obj); function removeArrayValues(obj) { for (var key in obj){ console.log(Array.isArray(obj[key])) if (Array.isArray(obj[key])) delete obj[key] //return obj[key] -> {b: 2, c: ["hi", "there"]} } return obj[key] } 

So, the first key will be removed ("true"), the second one will not ("false"), and the third one will be removed ("true").