for loop in Javascript

问题

for (let x of a) does not work in IE11. Can I replace it by for (let x in a) ?

for (let key in a) {  
    s += key + ": " + a[key];  
    s += "<br />";  
    }  

for (let key of a) {  
    s += key + ": " + a[key];  
    s += "<br />";  
    }  

回答1:

for...of is not supported in IE11 yet.

You can use for..in to iterate over as it has the support from IE6.

If you just want to add the key and value, you can use Object.keys and build the string that is needed.

let f = '';
let s = '';
let a = {
  firstName: 'Hello',
  lastName: 'JS',
  address: 'ecma'
};

for(let key in a) {
  s += key + ": " + a[key];
  s += "<br />";
}


Object.keys(a).forEach(function(key) {
  f += key + ": " + a[key];
  f += "<br />";
});

document.querySelector('.for-in').innerHTML = f;
document.querySelector('.object-keys').innerHTML = s;

.for-in {
  border: 1px solid green;
  min-height: 20px;
  padding: 20px;
}

.object-keys {
margin-top: 20px;
  border: 1px solid red;
  min-height: 20px;
  padding: 20px;
}

<div class="for-in">
</div>
<div class="object-keys">
</div>

回答2:

IE11 doesn't support for..of. Here's the compatibility table from MDN:

Another idiomatic option for this type of string building is via Array.prototype.reduce:

var string = Object.keys(a).reduce(function(acc, key) {
  return acc + key + ': ' + a[key] + '<br />';
}, '');

来源：https://stackoverflow.com/questions/46458493/for-loop-in-javascript