Understanding Javascript immutable variable -

i trying understand javascript immutable variable means. if can do:

var x = "astring"; x = "str"; console.log(x); //logs str` , why immutable? 

the answer can think (from little bit of c know) var x pointer memory block value "astring", , after 2nd statement points block value "str". case?

and bonus question: confused value types of javascript. variables objects under hood? number , strings?

values immutable; variables not; hold reference (primitive) values.

the 3 primitive types string, number , boolean have corresponding types instances objects: string, number, boolean.
called wrapper types.

the following values primitive:

• strings: "hello"
• numbers: 6, 3.14 (all numbers in javascript floating point)
• booleans: true, false
• null: explicitly assigned
• undefined: default (automatically assigned) value

all other values objects, including wrappers primitives.

so:

• objects mutable default
• objects have unique identities , compared reference
• variables hold references objects
• primitives immutable
• primitives compared value, don’t have individual identities

you might find the secret life of javascript primitives explanation.

also, in es6 there new const keyword, creates read-only named constant cannot change value through assignment or re-declared while script running.

hope helps!