javascript - Lodash 中的 partialRight 似乎什么都不做

Question

(我找不到 open Lodash Slack channel ，这就是我在这里发帖的原因。)

你能告诉我为什么这个fiddle中的partialRight吗？似乎什么都不做？ correctRenameKeys 函数正确地重命名了提供的 object 中的键，但是 wrongRenameKeys 函数(应该做的完全一样)却没有。

运行 fiddle 时，请在浏览器中打开 JavaScript 控制台以查看日志。我在 Chrome 中对其进行了测试。

    const renameKeysOfOneObject = (object, keyMappings) => {
      return _.reduce(object, function(result, value, key) {
        key = keyMappings[key] || key;
        result[key] = value;
        return result;
      }, {});
    };

    const correctRenameKeys = (objects, keyMappings) => {
        const keysRenamer = object => renameKeysOfOneObject(object, keyMappings);
        return _.map(objects, keysRenamer);
    };

    const wrongRenameKeys = (objects, keyMappings) => {
        const keysRenamer = _.partialRight(renameKeysOfOneObject, keyMappings);
        return _.map(objects, keysRenamer);
    };

    const object = {keyToBeRenamed: 'someValue'};
    const objects = [object];
    const keyMapping = {keyToBeRenamed: 'newKeyName'};

    const correctlyRenamed = correctRenameKeys(objects, keyMapping);
    const wronglyRenamed = wrongRenameKeys(objects, keyMapping);

    console.assert(_.isEqual(correctlyRenamed, wronglyRenamed), 
                   "The two objects should be equal. " + 
                   "The 'keyToBeRenamed' key should have been renamed to 'newKeyName'.");
    console.log(correctlyRenamed);
    console.log(wronglyRenamed);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>

Answer 1

lodash 文档中有两个支持语句可以回答您的问题:

lodash#partialRight

This method is like _.partial except that partially applied arguments are appended to the arguments it receives.

lodash#map

Creates an array of values by running each element in collection thru iteratee. The iteratee is invoked with three arguments: (value, index|key, collection).

请注意，在 lodash#map 迭代器中传递了三个参数，并且由于 keyRenamer 是作为迭代器传递的，因此我们可以得出结论，调用签名看起来像这样:

keyRenamer(value, index, collection, keyMappings);

如果您真的想实现部分应用函数 renameKeysOfOneObject 的第二个参数的效果，请使用 lodash#partial .

const wrongRenameKeys = (objects, keyMappings) => {
    const keysRenamer = _.partial(renameKeysOfOneObject, _, keyMappings);
    return _.map(objects, keysRenamer);
};

const renameKeysOfOneObject = (object, keyMappings) => {
      return _.reduce(object, function(result, value, key) {
        key = keyMappings[key] || key;
        result[key] = value;
        return result;
      }, {});
    };

    const correctRenameKeys = (objects, keyMappings) => {
        const keysRenamer = object => renameKeysOfOneObject(object, keyMappings);
        return _.map(objects, keysRenamer);
    };

    const wrongRenameKeys = (objects, keyMappings) => {
        const keysRenamer = _.partial(renameKeysOfOneObject, _, keyMappings);
        return _.map(objects, keysRenamer);
    };

    const object = {keyToBeRenamed: 'someValue'};
    const objects = [object];
    const keyMapping = {keyToBeRenamed: 'newKeyName'};

    const correctlyRenamed = correctRenameKeys(objects, keyMapping);
    const wronglyRenamed = wrongRenameKeys(objects, keyMapping);

    console.assert(_.isEqual(correctlyRenamed, wronglyRenamed), 
                   "The two objects should be equal. " + 
                   "The 'keyToBeRenamed' key should have been renamed to 'newKeyName'.");
    console.log(correctlyRenamed);
    console.log(wronglyRenamed);

.as-console-wrapper{min-height:100%;top:0}

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>