bind-deep

Bind Deep

Lightweight module for binding a function or object deeply

Description

Bind an object to this in all methods in a function, object, or array. A simple, single-dependency (only for TypeScript types) alternative to deep-bind.

Features

• Binds the root function and all own, enumerable property functions including property accessors
• Compatible with functions, arrays, objects, custom classes, and array-likes
• Binds the this value and optionally, additional arguments just like func.bind()
• Copies objects and enumerable properties deeply
• Preserves and copies prototypes for all types
• New in v2.1.0: Strict TypeScript type definitions

Installation

npm install bind-deep --save

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Usage

bindDeep(object, thisArg, [...args])

Returns: Function | Object | Array - The function or object passed as object but with itself and all methods bound to thisArg

Parameter	Type	Description
object	Function | Object | Array	Function or object to bind itself and all of its methods
thisArg	Object	The value bound to this for each bound function and method when called
[...args]	any	Arguments provided to the bound function when the bound function is invoked

Example

// Require bind-deep
const bindDeep = require("bind-deep");


// Original object and function
// Could also be an actual object
const func = function() {
    // Use `this`
};
func.method = function() {
    // Use `this` again
};

const obj = {
    method() {
        // Use `this`
    }
};


// Deeply bound object and function
// `thisArg` will be what every function and method will see as `this`
const boundObj = bindDeep(obj, thisArg);
// => {method: [Function: bound]}

const boundFunc = bindDeep(func, thisArg);
// => {[Function: bound] method: [Function: bound]}

TypeScript

All types inferred or annotated are preserved from the original functions and objects. The type definitions are incredibly strong deep types as the only negative side-effects are:

• If bound arguments are added, the arguments in call signatures are renamed by their bound position.
• If more than around 39 bound arguments are added, TypeScript will error Type instantiation is excessively deep and possibly infinite.
  • If you somehow do this, slap on an as any or your manually created type

An in-depth explanation is commented inside of index.d.ts and below with example code.

// Import bind-deep
import bindDeep from "bind-deep";


interface OriginalThis {
    discriminator: string;
}

// Original function
const myFunction = function (this: OriginalThis, arg1: string, arg2: number) {
    return this;
};
myFunction.method = function (this: OriginalThis, arg1: string) {
    return this;
};
myFunction.primitive = "string";

// `thisArg` value
const newThis = { newThis: "that's me!"};

// Deeply bound functions
const boundFunction = bindDeep(myFunction, newThis);
const boundFunctionWithArgs = bindDeep(myFunction, newThis, "add arg1 for each function");

/*
    Root call signature: `(arg1: string, arg2: number) => OriginalThis`
    - `this` argument type omitted from the original call signature as it is now bound
    - All other argument types and names are preserved
    - Returns `newThis` as `OriginalThis` due to the return value inferred by TypeScript
*/
boundFunction("arg1", 10); // returns `newThis`
/*
    Root call signature when passing an argument: `((args_0: number) => OriginalThis)`
    - Similar explanation to the root call signature
    - `arg1` argument type omitted from the original call signature as it is now bound
    - `arg2` is represented as `args_0` with the number type preserved
        - This unfortunate renaming only occurs when binding arguments
*/
boundFunctionWithArgs(10); // returns `newThis`

/*
    Method call signature: `(method) method(arg1: string): OriginalThis`
*/
boundFunction.method("arg1"); // returns `newThis`
/*
    Method call signature when passing an argument: `(method) method(): OriginalThis`
*/
boundFunctionWithArgs.method(); // returns `newThis`

/*
    Primitive property type: `primitive: string`
*/
const myString: string = boundFunction.primitive; // still "string", typings preserved

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License

Copyright Evelyn Hathaway, MIT License