ECMAScript Stage-0 Proposal. J. S. Choi, 2021.
- Formal specification: Not yet
- Babel plugin: Not yet
- Proposal history
The Function.prototype.unThis method creates a new function that calls the
original function, supplying its first argument as the original function’s
this receiver, and supplying the rest of its arguments as the original
function’s ordinary arguments.
This is useful for converting this-based functions
into non-this-based functions.
fn.unThis();
const $slice = Array.prototype.slice.unThis();
$slice([ 0, 1, 2 ], 1); // [ 1, 2 ].This is not a substitute for a bind-this syntax, which allows developers to change the receiver of functions without creating a wrapper function.
fn.unThis() is equivalent to
Function.prototype.call.bind(fn) and to
Function.prototype.bind.bind(Function.prototype.call)(fn).
Therefore, fn.unThis()(thisArg, ...restArgs) is equivalent to
fn.call(thisArg, ...restArgs).
The following real-world example originally used call-bind or a manually created similar function.
// From chrome-devtools-frontend@1.0.934332
// node_modules/array-includes/test/implementation.js.
runTests(implementation.unThis(), t);
// From string.prototype.trimstart@1.0.4/index.js:
var bound = getPolyfill().unThis();
// From andreasgal/dom.js (84b7ab6) src/snapshot.js.
const /* … */
join = A.join || Array.prototype.join.unThis(),
map = A.map || Array.prototype.map.unThis(),
push = A.push || Array.prototype.push.unThis(),
/* … */;Precedents include:
- call-bind:
callBind