There are lines in Underscore
_.clone = function(obj) {
if (!_.isObject(obj)) return obj;
return _.isArray(obj) ? obj.slice() : _.extend({}, obj);
};
And I have no idea why obj.slice() was used here to return a obj(array).
If _.isArray(obj) is true, the return becomes obj.slice().
As far as I know, array.slice without parameters does nothing. I think it should be just obj rather than obj.slice().
Is there any reason obj.slice() was used in this line?
This function should clone something, thus create a new array. If you return obj, there is no cloning at all. From the doc, array.slice():
returns a new array containing the extracted elements.
Calling slice() is a simple way to make a copy of the array. But note that this method only performs a shallow copy (vs a deep copy): with nested arrays (or arrays of objects), the items will keep the same address. Here is a simple example:
var o1 = {"name": "henry"};
var o2 = {"name": "jean"};
var a1 = [o1, o2];
var a2 = a1.slice();
a2[0].name = "modified";
console.log(a1[0].name); // --> "modified"
console.log(a1[0] === a2[0], a1[0] === o1); // --> true
