Convert var to let or const
Replace var
with block-scoped variables let
and const
.

let
and const
are block-scope variable declarations that can replace 'var' declarations in many cases.
const
declares blocked-scoped variables that cannot be re-assigned. let
declares block-scoped variables that can be changed.
They are available since ES6 and are preferred over function-scope, modifiable var
declarations, because they make it easier to reason about the code.
When there are several variables declared in a statement, this refactoring does not change the declaration to prevent formatting breakages and linter issues.
What do I need to consider?
Top-level var
declarations can define global variables visible in other files and script sections in some environments.
Most environments (e.g., Node.js), TypeScript code generation, bundling, and ECMAScript Modules prevent this behavior and expect you to use globalThis
or its variants to define a global variable.
However, when you directly include scripts in the browser using the script tag (<script src="a-script.js"></script>
), var
could define globals, and converting to let
or const
could break your code.