So I've tried to use the map() method as follows:
words = ["One", "Two"];
words = words.map(function(currentValue)
{
alert(currentValue[0]);//Output: O Then: T
currentValue[0] = "A";
alert(currentValue[0]);//Output: O Then: T
return currentValue;
});
Why is it that currentValue[0] is not getting assigned the value "A"?!?
Your attempting to assign to a string at a specific position via its index, this is not possible as Strings are immutable. If you want to change a string you need to create a new one.
string[pos] syntax but you cannot write to the string - if you could do that you would have a string that contained a different value from the one it was created with, and JavaScript disallows this (immutability).As Alex K correctly points out, strings are immutable and you cannot modify them.
Since you are using a .map(), the thing to do here is just construct a new string and return that:
var words = ["One", "Two"];
words = words.map(function (currentValue) {
return "A" + currentValue.substring(1);
});
console.log(words); // outputs ["Ane", "Awo"];
As a rule of thumb, you should not try to use .map() to modify existing values. The purpose of .map() is to produce a new set of values, and leave the original ones untouched.
In JavaScript String is the primitive type, so you cannot mutate it.
String , Number , Boolean, Null, Undefined, Symbol (new in ECMAScript 6) are primitive types.
"" instanceof Object produces false. See: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…