1.1.3 • Public • Published


SBO stands for Support the Bind Operator.

Converts value::yourFunction(arg) to yourFunction(value, arg)—but lets your function support either.


Requires Node.js 6.0.0 or above.

npm i sbo


The module exports a single function.


  1. Optional: Object argument:
    • Optional: arg (integer): The argument index at which this should be inserted. Defaults to 0.
    • Optional: path (string): The dot-separated key path of an options object argument located at index arg into which this should be inserted.
    • Optional: ignoreThis (object, array, or function): this is ignored if ignoreThis strictly equals this, or if ignoreThis is an array containing this, or if ignoreThis is a function which returns true when given this.
  2. fn (Function): The function which should receive bind operator support.

Return Value

A wrapper function with bind operator support that calls fn.


Let’s say, for the sake of example, that you have a function called addSuffix:

const addSuffix = (str, suffix) => str + suffix

You use the sbo module to add support for the bind operator:

const supportBindOperator = require('sbo')
const addSuffix = supportBindOperator((str, suffix) => str + suffix)

Now your function can be called either the normal way or with the bind operator:

addSuffix('Hello, world', '!') // 'Hello, world!'
'Hello, world'::addSuffix('!') // 'Hello, world!'

Specifying a Parameter Index

Now let’s swap the order of the parameters:

const addSuffix = (suffix, str) => str + suffix

A bound this would now need to become the argument with an index of 1. To do this, pass an extra argument to sbo:

const supportBindOperator = require('sbo')
const addSuffix = supportBindOperator({arg: 1}, (suffix, str) => str + suffix)

addSuffix('!', 'Hello, world') // 'Hello, world!'
'Hello, world'::addSuffix('!') // 'Hello, world!'

Specifying an Object Argument Key

Let’s try using a deconstructed object parameter:

const addSuffix = ({str, suffix}) => str + suffix

Do the following to direct a bound this to the str key of the object argument at index zero (i.e. the first, and in this case the only, argument):

const supportBindOperator = require('sbo')
const addSuffix = supportBindOperator({path: 'str'}, ({str, suffix}) => str + suffix)

addSuffix({str: 'Hello, world', suffix: '!'}) // 'Hello, world!'
'Hello, world'::addSuffix({suffix: '!'}) // 'Hello, world!'

If you have a nested object parameter, you can use a dot-separated key path.


Check out these other function utility packages.

  • efn: Extracted Function
  • ffn: Filtering Function
  • jfn: Joined Function
  • mfn: Memoized Function
  • ofn: Overloaded Function
  • pfn: Possible Function
  • qfn: Qualified Function
  • vfn: Variadic Function
  • wfn: Wrapper Function
  • xfn: Extended Function
  • 3fn: Three-Way Comparison Function

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npm i sbo

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  • lamansky