- Welcome to Getting Started With ES2015 1:01
- Declaring Variables in JavaScript 1:20
- Creating Unchanging Variables With const 4:10
- Using Constants with Arrays and Objects 2:44
- Review creating variables with const 5 questions
- Defining a Variable with let 2:48
- Using let with for Loops 2:25
- Reviewing let and const 1:00
- Review let and const 5 questions
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Using Constants with Arrays and Objects
2:44Using constants prevents values from being reassigned but how do they work with arrays and objects?
We've seen that you cannot reassign a
constant variable in the case of a number
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or a string.
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The same goes for
any value of a constant variable.
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You cannot reassign strings, numbers,
booleans, objects, and arrays.
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Unlike strings, numbers and booleans,
objects in arrays have methods and
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properties that modify the objects or
array.
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Do they still work with const?
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First, we'll declare a variable
which is a constant called days.
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This will contain an array
with a single string, Monday.
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Second, we'll declare
another constant variable,
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person, that contains an object's literal
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with a first_name key,
with the string Imogen.
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Let's attempt to modify
these in the console here.
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First, days, Let's use the push method
to add another date to the array.
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It didn't error.
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It returned the number 2,
meaning the new array length.
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If we type days and hit Enter,
we get Monday and Tuesday returned.
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Let's try and add a last_name property
to the person object, Again no error.
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When we type person and hit Enter,
we get an object literal back
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with the first_name and
last_name properties.
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So what's happening here?
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Const doesn't prevent complex objects like
arrays and objects from being modified.
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It just prevents them from being
reassigned or overwritten completely.
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For example, when I attempt to overwrite
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person with another object literal.
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It shows an error, because I'm attempting
to reassign person with a new object.
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However, if I modified the first_name,
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To equal another value,
Andrew, I don't get any errors.
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