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JavaScript JavaScript Arrays Multidimensional Arrays What is a Multidimensional Array?

karan Badhwar
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karan Badhwar
Web Development Techdegree Graduate 18,135 Points
Posted by karan Badhwar
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karan Badhwar
Web Development Techdegree Graduate 18,135 Points

Array with const

How are we able to change the values in an array even if it was declared with const keyword?

Variables will throw an error, but why an array does not?

1 Answer

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

The "const" only applies to the array itself, not the elements inside it.

You'll still get the error if you try to reassign the array:

const a = [1, 2, 3];
a[2] = 9;    // this is OK
a = 999;     // but this causes: "TypeError: Assignment to constant variable."
karan Badhwar
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
karan Badhwar
Web Development Techdegree Graduate 18,135 Points
karan Badhwar
.a{fill-rule:evenodd;}techdegree seal-36
karan Badhwar
Web Development Techdegree Graduate 18,135 Points

But how are we even able to change the values as well? As, when we assign the variable with const we cannot change the value, but we change specific values of arrays, but cannot change the whole value? why so?

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

As I said, "const" only protects the variable you declare with it. It does not protect anything inside that variable (like array elements or object properties).

There is a way to protect the contents also, called "freezing", but it's rather obscure. Example:

const a = [1, 2, 3];
Object.freeze(a);
a[2] = 999;      // no error, but nothing happens
console.log(a);  // it still has [1,2,3]