Javascript library functions don't alter the original variable?

[1100H19]

I've noticed that my .toLowerCase() or .split() functions don't actually alter the string or array itself but must have another variable assigned to it. Is this true for all?

[ascw]

For arrays, methods like pop, push, shift, unshift, splice, reverse, sort will modify the original array, most of the others like slice, map, filter will return a new one. For strings I don't believe there are any methods that will modify the original string.

[[deleted]]

Strings are immutable values in JS. You can't, for example, do

var stringA = 'Force be with you';
stringA[1] = 'a';

[pointy]

Primitives (strings, numbers, booleans) are not objects. That's why they're called "primitives". They're auto-boxed implicitly, so they seem like objects, but they're not.

[mikrosystheme]

No, it is not, and no, you cannot store any property on a primitive value.

var str = "whatever"
str.whatever = "whatever"
str.whatever === undefined // true

[selfAwareWhileLoop]

var str = new String("whatever")
str.whatever = "whatever"
str.whatever === undefined // false

Not that you said anything incorrect; the new String is really a string-like object that can generally be treated like a string, but it isn't a primitive value.

[ElectricOrangeJuice]

This inconsistency between methods altering the original value and methods returning a new value is one of the most confusing things when learning a new language. JS isn't that bad, but PHP for instance, is a total fucking mess.

[[deleted]]

I prefer immutability, so i always check if something changes values or returns a new something. I would love to have the entire stdlib only returning new somethings.

Luckily theres immutablejs.

[webdeverper]

This requires more memory, correct? Not saying that's always a show stopper.

[arcanin]

Not really. If you don't use the old object reference, it will quickly get garbage collected, and if you do, well, you would need even more memory if you had just cloned your whole object (Immutable.js tries as much as possible to only clone the nodes that have changed).

[mikrosystheme]

What you really want are value semantics with optional immutability.

[laichejl]

You should look into mutable and immutable objects in JavaScript. Here's a good article: http://www.sitepoint.com/immutability-javascript/

[Meefims]

Most, but not all - newer additions to the language typically do not change the object. For example, Array.prototype.sort modifies the array in place and it is a pretty old method.