new Number() vs Number()
What is the difference between new Number() and Number()? I get that new Number() creates a Number object and Number() is just a function, but when should I call which, and why?
On a related note, Mozilla says:
Do not use a Boolean object to convert a non-boolean value to a boolean value. Instead, use Boolean as a function to perform this task.
x = Boolean(expression); // preferred
x = new Boolean(expression); // don't useWhy is that? I thought the results were the same?
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Boolean(expression) will simply convert the expression into a boolean primitive value, while new Boolean(expression) will create a wrapper object around the converted boolean value.
The difference can be seen with this:
// Note I'm using strict-equals
new Boolean("true") === true; // false
Boolean("true") === true; // trueAnd also with this (thanks @hobbs):
typeof new Boolean("true"); // "object"
typeof Boolean("true"); // "boolean"Note: While the wrapper object will get converted to the primitive automatically when necessary (and vice versa), there is only one case I can think of where you would want to use new Boolean, or any of the other wrappers for primitives - if you want to attach properties to a single value. E.g:
var b = new Boolean(true);
b.relatedMessage = "this should be true initially";
alert(b.relatedMessage); // will work
var b = true;
b.relatedMessage = "this should be true initially";
alert(b.relatedMessage); // undefined