bind2

Enhanced Javascript bind() function.

Why ?

Because the [[BoundThis]] internal properties of a bound function are not programmatically accessible, and you might need to get the context of a function without executing it. This lib also provides some tooling around the bind mechanism.

Features

• Does not break the original bind API.
• Immutable.
• New properties assigned to each bound function (using bind2()) :
  • unbind() (Function). Will return the original unbound function.
  • unbound (Function). Reference to the original unbound function.
  • context (Any). Get the function context without executing it.
  • bound (Boolean). Returns true if the function has been bound with bind2.
  • bind2(context, ...parameters) (Function). Re-bind the function. (Note : bind() still exists.)

Examples

const bind2 = require('bind2');
 
function test() {
  return this.hello;
}
const context = { hello: 'world' };
 
// Native `bind()`.
const boundFn = test.bind(context);
console.log(boundFn.context); // undefined
console.log(boundFn.bound); // undefined
console.log(bound2Fn.unbound); // undefined
console.log(bound2Fn.unbind()); // TypeError: bound2Fn.unbind is not a function
console.log(boundFn()); // 'world'
 
// `bind2()`.
const bound2Fn = bind2(test, context);
console.log(bound2Fn.context); // { hello: 'world' }
console.log(bound2Fn.bound); // true
console.log(bound2Fn.unbound); // [Function: test]
console.log(bound2Fn.unbind()); // [Function: test]
console.log(bound2Fn()); // 'world'

API

const bind2 = require('bind2');

bind2(fn, thisArg[, arg1[, arg2[, ...]]])

This function is a wrapper the native bind() function.

• Arguments :

  • fn (Function) : the function to bind.
  • thisArg : The value to be passed as the this parameter to the target function when the bound function is called. The value is ignored if the bound function is constructed using the new operator. When using bind to create a function (supplied as a callback) inside a setTimeout, any primitive value passed as thisArg is converted to object. If no arguments are provided to bind, the this of the executing scope is treated as the thisArg for the new function.
  • arg1, arg2, ... : Arguments to prepend to arguments provided to the bound function when invoking the target function.

• Returns : a copy of the given function with the specified this value and initial arguments.

bind2.fn(fn, thisArg[, arg1[, arg2[, ...]]])

Alias to bind2(fn, thisArg[, arg1[, arg2[, ...]]]).

bind2.define()

Alias to bind2.wrap(Function.prototype).

This will mutate the Function's prototype, thus adding the bind2() and bound properties to every function. It is recommended to execute this once, in the beginning of the script.

e.g.:

const bind2 = require('bind2');
 
// Wrap `Function.prototype`.
bind2.define();
 
function test() {
  return this.hello;
}
const context = { hello: 'world' };
 
// Use the new `bind2()` function.
const boundFn = test.bind2(context);
console.log(boundFn.context); // { hello: 'world' }

License

MIT

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