_.get() polyfill for the lodash.js method not available in underscore.js ~ fairly q&d implementation

_.get.js

// 28 June 2017
// Quick-and-dirty implementation.

// 30 Sept 2021
// Changes prompted by @nativekar:
// - Allow pathName param to be either Array or string.
// - Support "value[property]" notation.

// House-cleaning:
// - Move the inline mocha suite to own file, replace with inline test closure.
// - Add "_" inline definition for standalone test execution.
// Uncomment to set _ in test environment:
// var _ = globalThis._ ?? {};

/**
 * _.get() polyfill for q&d implementation.
 * lodash has _.get(data, path, defaultValue), but underscore does not.
 * makes data traversal so nice.
 * see https://lodash.com/docs/4.17.4#get
 */
typeof _.get == 'function' || (function() {
  /**
   * @param {object} object, The object to query.
   * @param {Array|string} pathName: The path of the property to get.
   * @param {*} [defaultValue]: Optional value to return for undefined resolved values.
   * @returns {*} resolved value, or default value if specified.
   */
  var at = function get(object, pathName, defaultValue) {
    
    // Coerce pathName to a string (even it turns into "[object Object]").
    var path = Array.isArray(pathName)
      ? pathName.join(".")
      : String(pathName);
    
    // Support bracket notation, e.g., "a[0].b.c".
    var match = /\[\\?("|')?(\w|d)+\\?("|')?\]/g;
    
    var parts = path
      .replace(match, (m, i, v) => "." + v)
      .split('.');

    var length = parts.length;
    var i = 0;

    // In case object isn't a real object, set it to undefined.
    var value = object === Object(object) ? object : undefined;

    while (value != null && i < length) {
      value = value[parts[i++]];
    }

    /**
     * lodash.get() returns the resolved value if
     * 1. iteration happened (i > 0)
     * 2. iteration completed (i === length)
     * 3. the value at the path is found in the data structure (not undefined). Note that if the path is found but the
     *    value is null, then null is returned.
     * If any of those checks fails, return the defaultValue param, if provided.
     */
    return i && i === length && value !== undefined ? value : defaultValue;
  };

  _.get = at;
}());

/* test it out */

~(function suite() {
  
  // suite replaces inline mocha suite which has been moved to its own file.
  
  var data = { a: { b: { c: { d: 'hello' } } } };
  var defaultValue = "I'm the default value";
  var unresolved = 'not resolved';
  var expected = 6;
  var instance = Object(1);

  var tests = [
    // should find value by pathName.
    _.get(data, 'a.b.c.d') === 'hello',
    
    // should return default value when pathName not resolved.
    _.get({}, 'a.b.c.d', defaultValue) === defaultValue,
    
    // should not resolve non-object data.
    _.get('1', 'toString', unresolved) === unresolved,
    
    // should not resolve with an invalid pathName.
    _.get({ name: 'hello' }, '', unresolved) === unresolved,
        
    // should resolve on arrays with valid index pathName.
    _.get([1, 2, [3, 4, [5, expected]]], '2.2.1', expected) === expected,
    
    // should resolve on coerced-to-an-object with valid pathName.
    _.get(instance, 'toString').call(instance) === "1",
    
    // should resolve pathName as an Array of descendant property names.
    _.get(data, ['a', 'b', 'c', 'd']) === 'hello',
    
    // should resolve pathName containing bracket property names.
    _.get(data, 'a["b"]["c"]["d"]') === 'hello',

    // should resolve pathName containing bracket property names.
    _.get(data, ['a["b"]', 'c', 'd']) === 'hello'
  ];

  // Should print array with all values `true`.
  console.log( tests );
}());

_.test-get.js

// 30 Sept 2021
// moved the inline mocha suite to own file

describe('_.get() method', function() {
  
  /**
   * Verification of the _.get() utility method.
   * using mocha and chai.assert
   */
  
  it('should find value by path', function (done) {
    var data = {
      a: {
        b: {
          c: {
            d: 'hello'
          }
        }
      }
    };
    var value = _.get(data, 'a.b.c.d');

    assert.equal(value, 'hello');
    done();
  });

  it('should return default value when path not resolved', function (done) {
    var defaultValue = "I'm the default value";
    var value = _.get({}, 'a.b.c.d', defaultValue);

    assert.equal(value, defaultValue);
    done();
  });

  it('should not resolve non-object data', function (done) {
    var unresolved = 'not resolved';
    var value = _.get('1', 'toString', unresolved);

    assert.equal(value, unresolved);
    done();
  });

  it('should not resolve with an invalid pathString', function (done) {
    var unresolved = 'not resolved';
    var value = _.get({ name: 'hello' }, '', unresolved);

    assert.equal(value, unresolved);
    done();
  });

  it('should resolve on arrays with valid index pathString', function(done) {
    var expected = 6;
    var value = _.get([1, 2, [3, 4, [5, expected]]], '2.2.1', expected);

    assert.equal(value, expected);
    done();
  });

  it('should resolve on coerced-to-an-object with valid pathString', function (done) {
    var instance = Object(1);
    var value = _.get(instance, 'toString');

    // it's a function, try to call it
    assert.strictEqual(value.call(instance), '1');
    assert.notStrictEqual(value.call(instance), 1);

    // coerced toString output
    assert.equal(value, 'function toString() { [native code] }');
    done();
  });
});

using this, thanks!

The 2nd argument, pathString isn't always a String. Most of the time, it can also be an array.

@nativekar I wasn’t aware of that. But then I haven’t used this in a long time. Might fix this in a couple days.

Thanks for pointing it out.

Cheers! Look forward to the fix. (I have started working on one of mine, maybe we can compare notes)

@nativekar - OK, I've updated the method to accept arrays as pathName params, added support for value[property] notation, and redone the inline tests as a closure (and moved the mocha suite to its own file). Let me know if you have questions.

@dfkaye - this looks perfect. Thanks for working on this.

@nativekar - Thanks. So, I looked up underscore docs to see if they had a get method now - turns out they do - https://underscorejs.org/#get - oh well…