Immutability
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
. The 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:
2 1
As you can see, the results for the constant and variable are different.
If you're using an older browser without support, then const
won't be available ...
Get JavaScript: Moving to ES2015 now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.