lodash/test/partial-methods.js

import assert from 'assert';
import lodashStable from 'lodash';
import { _, identity, slice } from './utils.js';
import placeholder from '../placeholder.js';
import curry from '../curry.js';

describe('partial methods', function() {
  lodashStable.each(['partial', 'partialRight'], function(methodName) {
    var func = _[methodName],
        isPartial = methodName == 'partial',
        ph = func.placeholder;

    it('`_.' + methodName + '` partially applies arguments', function() {
      var par = func(identity, 'a');
      assert.strictEqual(par(), 'a');
    });

    it('`_.' + methodName + '` creates a function that can be invoked with additional arguments', function() {
      var fn = function(a, b) { return [a, b]; },
          par = func(fn, 'a'),
          expected = isPartial ? ['a', 'b'] : ['b', 'a'];

      assert.deepStrictEqual(par('b'), expected);
    });

    it('`_.' + methodName + '` works when there are no partially applied arguments and the created function is invoked without additional arguments', function() {
      var fn = function() { return arguments.length; },
          par = func(fn);

      assert.strictEqual(par(), 0);
    });

    it('`_.' + methodName + '` works when there are no partially applied arguments and the created function is invoked with additional arguments', function() {
      var par = func(identity);
      assert.strictEqual(par('a'), 'a');
    });

    it('`_.' + methodName + '` should support placeholders', function() {
      var fn = function() { return slice.call(arguments); },
          par = func(fn, ph, 'b', ph);

      assert.deepStrictEqual(par('a', 'c'), ['a', 'b', 'c']);
      assert.deepStrictEqual(par('a'), ['a', 'b', undefined]);
      assert.deepStrictEqual(par(), [undefined, 'b', undefined]);

      if (isPartial) {
        assert.deepStrictEqual(par('a', 'c', 'd'), ['a', 'b', 'c', 'd']);
      } else {
        par = func(fn, ph, 'c', ph);
        assert.deepStrictEqual(par('a', 'b', 'd'), ['a', 'b', 'c', 'd']);
      }
    });

    it('`_.' + methodName + '` should use `_.placeholder` when set', function() {
      var _ph = placeholder = {},
          fn = function() { return slice.call(arguments); },
          par = func(fn, _ph, 'b', ph),
          expected = isPartial ? ['a', 'b', ph, 'c'] : ['a', 'c', 'b', ph];

      assert.deepEqual(par('a', 'c'), expected);
      delete placeholder;
    });

    it('`_.' + methodName + '` creates a function with a `length` of `0`', function() {
      var fn = function(a, b, c) {},
          par = func(fn, 'a');

      assert.strictEqual(par.length, 0);
    });

    it('`_.' + methodName + '` should ensure `new par` is an instance of `func`', function() {
      function Foo(value) {
        return value && object;
      }

      var object = {},
          par = func(Foo);

      assert.ok(new par instanceof Foo);
      assert.strictEqual(new par(true), object);
    });

    it('`_.' + methodName + '` should clone metadata for created functions', function() {
      function greet(greeting, name) {
        return greeting + ' ' + name;
      }

      var par1 = func(greet, 'hi'),
          par2 = func(par1, 'barney'),
          par3 = func(par1, 'pebbles');

      assert.strictEqual(par1('fred'), isPartial ? 'hi fred' : 'fred hi');
      assert.strictEqual(par2(), isPartial ? 'hi barney'  : 'barney hi');
      assert.strictEqual(par3(), isPartial ? 'hi pebbles' : 'pebbles hi');
    });

    it('`_.' + methodName + '` should work with curried functions', function() {
      var fn = function(a, b, c) { return a + b + c; },
          curried = curry(func(fn, 1), 2);

      assert.strictEqual(curried(2, 3), 6);
      assert.strictEqual(curried(2)(3), 6);
    });

    it('should work with placeholders and curried functions', function() {
      var fn = function() { return slice.call(arguments); },
          curried = curry(fn),
          par = func(curried, ph, 'b', ph, 'd');

      assert.deepStrictEqual(par('a', 'c'), ['a', 'b', 'c', 'd']);
    });
  });
});