bind.js

var R = require('../source/index.js');
var eq = require('./shared/eq.js');


describe('bind', function() {

  function Foo(x) {
    this.x = x;
  }
  function add(x) {
    return this.x + x;
  }
  function Bar(x, y) {
    this.x = x;
    this.y = y;
  }
  Bar.prototype = new Foo();
  Bar.prototype.getX = function() {
    return 'prototype getX';
  };

  it('returns a function', function() {
    eq(typeof R.bind(add, Foo), 'function');
  });

  it('returns a function bound to the specified context object', function() {
    var f = new Foo(12);
    function isFoo() {
      return this instanceof Foo;
    }
    var isFooBound = R.bind(isFoo, f);
    eq(isFoo(), false);
    eq(isFooBound(), true);
  });

  it('works with built-in types', function() {
    var abc = R.bind(String.prototype.toLowerCase, 'ABCDEFG');
    eq(typeof abc, 'function');
    eq(abc(), 'abcdefg');
  });

  it('works with user-defined types', function() {
    var f = new Foo(12);
    function getX() {
      return this.x;
    }
    var getXFooBound = R.bind(getX, f);
    eq(getXFooBound(), 12);
  });

  it('works with plain objects', function() {
    var pojso = {
      x: 100
    };
    function incThis() {
      return this.x + 1;
    }
    var incPojso = R.bind(incThis, pojso);
    eq(typeof incPojso, 'function');
    eq(incPojso(), 101);
  });

  it('does not interfere with existing object methods', function() {
    var b = new Bar('a', 'b');
    function getX() {
      return this.x;
    }
    var getXBarBound = R.bind(getX, b);
    eq(b.getX(), 'prototype getX');
    eq(getXBarBound(), 'a');
  });

  it('preserves arity', function() {
    var f0 = function() { return 0; };
    var f1 = function(a) { return a; };
    var f2 = function(a, b) { return a + b; };
    var f3 = function(a, b, c) { return a + b + c; };

    eq(R.bind(f0, {}).length, 0);
    eq(R.bind(f1, {}).length, 1);
    eq(R.bind(f2, {}).length, 2);
    eq(R.bind(f3, {}).length, 3);
  });

});