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Tap and Thru in JavaScript

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[前端(javascript) 所属分类 前端(javascript) | 发布者 店小二03 | 时间 2016 | 作者 红领巾 ] 0人收藏点击收藏

Debugging chained methods and doing custom modifications is often troublesome. But by knowing the tap and thru methods, this is made significantly easier. Firstly, thru is used to get the current value in the chain and to return a newly modified one. Using Lodash’s chained example by using my chain function:

var result = chain(' abc ') .trim() .thru(function(value) { return [value]; }) .value(); console.log(result); // ['abc']

Since the value is returned, this allows any type of modification to occur as long as it is synchronous. Tap just gives the value and expects no return (similar example to the Lodash site):

var result = chain([1, 2, 3]) .tap(function(array) { array.pop(); }) .reverse() .value(); console.log(result);

In most cases this is not as useful as thru because it will not allow primitive values like strings to be modified. But it is more convenient for debugging since no return needs to be used:

var result = chain([1, 2, 3]) .reverse() .tap(function(array) { console.log(‘Reversed array is:’, array); }) .value();

So using these patterns will make doing modifications not in the chained methods possible as well as providing much easier debugging. Additionally, any time you create a custom chain these two methods can be quickly added. For the above examples, I added them to my own simple chained object (since my posts usually do not rely on libraries):

var chain = function(value) { var self = {}; self.trim = function() { value = (value + '').trim(); return self; }; // Making this string based only for demonstration self.reverse = function() { value = value.reverse(); return self; }; self.tap = function(callback) { callback(value); return self; }; self.thru = function(callback) { value = callback(value); return self; }; self.value = function() { return value; }; return self; };

The tap and thru methods are available in Lodash.

Github Location: https://github.com/Jacob-Friesen/obscurejs/blob/master/2016/tap.js

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