微信小程序使用第三方库Underscore.js步骤详解

2019-11-20 08:52:16

字体：大中小

来源：转载

供稿：网友

前言

Underscore.js是一个很精干的库，压缩后只有4KB。Underscore 提供了100多个函数，包括常用的：map、filter、invoke ― 当然还有更多专业的辅助函数，如：函数绑定、JavaScript 模板功能、创建快速索引、强类型相等测试等等。弥补了标准库的不足，大大方便了JavaScript的编程。

微信小程序无法直接使用require( 'underscore.js' )进行调用。

微信小程序模块化机制

微信小程序运行环境支持CommoJS模块化，通过module.exports暴露对象，通过require来获取对象。

微信小程序Quick Start utils/util.js

function formatTime(date) { var year = date.getFullYear() var month = date.getMonth() + 1 var day = date.getDate() var hour = date.getHours() var minute = date.getMinutes() var second = date.getSeconds(); return [year, month, day].map(formatNumber).join('/') + ' ' + [hour, minute, second].map(formatNumber).join(':')}function formatNumber(n) { n = n.toString() return n[1] ? n : '0' + n}module.exports = { formatTime: formatTime}

pages/log/log.js

var util = require('../../utils/util.js')Page({ data: { logs: [] }, onLoad: function () { this.setData({ logs: (wx.getStorageSync('logs') || []).map(function (log) { return util.formatTime(new Date(log)) }) }) }})

原因分析

Underscore CommonJs模块导出代码如下：

// Export the Underscore object for **Node.js**, with// backwards-compatibility for the old `require()` API. If we're in// the browser, add `_` as a global object.if (typeof exports !== 'undefined') { if (typeof module !== 'undefined' && module.exports) { exports = module.exports = _; } exports._ = _;} else { root._ = _;}

exports、module必须都有定义，才能导出。通过测试，微信小程序运行环境exports、module并没有定义

//index.js//获取应用实例var app = getApp();Page({  onLoad: function () { console.log('onLoad'); var that = this; console.log('typeof exports: ' + typeof exports);  console.log('typeof module: ' + typeof exports);  var MyClass = function() { } module.exports = MyClass; console.log('typeof module.exports: ' + typeof module.exports);  }})

解决方法

修改Underscore代码，注释原有模块导出语句，使用module.exports = _ 强制导出

 /* // Export the Underscore object for **Node.js**, with // backwards-compatibility for the old `require()` API. If we're in // the browser, add `_` as a global object. if (typeof exports !== 'undefined') { if (typeof module !== 'undefined' && module.exports) { exports = module.exports = _; } exports._ = _; } else { root._ = _; } */ module.exports = _;

 /* // AMD registration happens at the end for compatibility with AMD loaders // that may not enforce next-turn semantics on modules. Even though general // practice for AMD registration is to be anonymous, underscore registers // as a named module because, like jQuery, it is a base library that is // popular enough to be bundled in a third party lib, but not be part of // an AMD load request. Those cases could generate an error when an // anonymous define() is called outside of a loader request. if (typeof define === 'function' && define.amd) { define('underscore', [], function() { return _; }); } */

使用Underscore.js

//index.jsvar _ = require( '../../libs/underscore/underscore.modified.js' );//获取应用实例var app = getApp();Page( { onLoad: function() { //console.log('onLoad'); var that = this; var lines = []; lines.push( "_.map([1, 2, 3], function(num){ return num * 3; });" ); lines.push( _.map( [ 1, 2, 3 ], function( num ) { return num * 3; }) ); lines.push( "var sum = _.reduce([1, 2, 3], function(memo, num){ return memo + num; }, 0);" ); lines.push( _.reduce( [ 1, 2, 3 ], function( memo, num ) { return memo + num; }, 0 ) ); lines.push( "var even = _.find([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });" ); lines.push( _.find( [ 1, 2, 3, 4, 5, 6 ], function( num ) { return num % 2 == 0; }) ); lines.push( "_.sortBy([1, 2, 3, 4, 5, 6], function(num){ return Math.sin(num); });" ); lines.push( _.sortBy( [ 1, 2, 3, 4, 5, 6 ], function( num ) { return Math.sin( num ); }) ); lines.push( "_.indexOf([1, 2, 3], 2);" ); lines.push( _.indexOf([1, 2, 3], 2) ); this.setData( {  text: lines.join( '/n' ) }) }})