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Getting Started With ES2015

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Using Constants with Arrays and Objects

2:44 with Andrew Chalkley

Using constants prevents values from being reassigned but how do they work with arrays and objects?

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    We've seen that you cannot reassign a constant variable in the case of a number 0:00
    or a string. 0:04
    The same goes for any value of a constant variable. 0:05
    You cannot reassign strings, numbers, booleans, objects, and arrays. 0:08
    Unlike strings, numbers and booleans, objects in arrays have methods and 0:14
    properties that modify the objects or array. 0:18
    Do they still work with const? 0:22
    First, we'll declare a variable which is a constant called days. 0:24
    This will contain an array with a single string, Monday. 0:33
    Second, we'll declare another constant variable, 0:39
    person, that contains an object's literal 0:45
    with a first_name key, with the string Imogen. 0:51
    Let's attempt to modify these in the console here. 0:59
    First, days, Let's use the push method to add another date to the array. 1:02
    It didn't error. 1:14
    It returned the number 2, meaning the new array length. 1:16
    If we type days and hit Enter, we get Monday and Tuesday returned. 1:21
    Let's try and add a last_name property to the person object, Again no error. 1:28
    When we type person and hit Enter, we get an object literal back 1:38
    with the first_name and last_name properties. 1:42
    So what's happening here? 1:47
    Const doesn't prevent complex objects like arrays and objects from being modified. 1:49
    It just prevents them from being reassigned or overwritten completely. 1:55
    For example, when I attempt to overwrite 2:00
    person with another object literal. 2:06
    It shows an error, because I'm attempting to reassign person with a new object. 2:16
    However, if I modified the first_name, 2:25
    To equal another value, Andrew, I don't get any errors. 2:32

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