One of the cornerstones of functional programming is that so called variables can be assigned only once. This is known as immutability. ECMAScript 2015 supports a new keyword,
const keyword can be used in the same way as
var except that variables assigned with
const will be immutable. For instance, the following code shows a variable and a constant that are both manipulated in the same way:
let numberOfQueens = 1; const numberOfKings = 1; numberOfQueens++; numberOfKings++; console.log(numberOfQueens); console.log(numberOfKings);
The output of running this is the following:
As you can see, the results for the constant and variable are different.
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