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May 26, 2020 19:09
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Immutable vs Mutable in JS - the immutable (unable to change or mutate) values are primitive values - numbers, strings, booleans, null, undefined). While the mutable are all other objects. They are generally referred to as reference types because the object values are references to the location, in memory, that the value resides.
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// start with at string | |
var s = "my string"; | |
//change its value (remember this changing of value is by value not reference) | |
s.toUpperCase(); | |
// assign it to t | |
var t = s; | |
//t is now "my string" | |
//this is because, when we changed the value of s to be uppercase, we were actually only referring to s's value not the | |
// location in which it is stored. Therefore the next time it is fetched, it is the same as the originally stored value | |
//objects on the other hand are reference types so when we mutate them, we are mutating the value that is stored in memory | |
//so the next time it is use, it will pull the value from memory with the mutations included | |
//create and mutate | |
var obj = { z : 1 }; | |
obj.y = 2; | |
obj.x = 3; | |
// obj, in memory, now stores all three properties | |
// a weird thing to come across is that because this is by reference, when you assign it to a new object like: | |
var otherObj = obj; | |
//otherObj is now pointing at the same location that obj is | |
//so changing any properties in otherObj will change them in obj, and vice versa | |
otherObj.a = 4; | |
//obj will also have a property named a with the value of 4 | |
//if you don't want this you must create a new object and explicitly copy over the properties | |
var finalObj = {}; | |
//- foreach property in obj | |
for(prop in obj){ | |
//add it to the new object | |
finalObj[prop] = obj[prop]; | |
} | |
great
good i learned very easily
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In short @pritambhanji, you're NOT changing the value of the string, you're changing the assignment of the variable. myString can change to any number of things, but "Pritam" still equals "Pritam".