微信小程序使用第三方库Underscore.js步骤详解

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

rush: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

rush: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：

rush:js;"> // 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

rush:js;"> //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

rush:js;"> /* // 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 = _;

rush:js;"> /* // 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

rush:js;"> //index.js

var _ = 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( [ 1,3 ],function( num ) { return num 3; }) );

lines.push( "var sum = _.reduce([1,function(memo,num){ return memo + num; },0);" );
lines.push( _.reduce( [ 1,function( memo,num ) { return memo + num; },0 ) );

lines.push( "var even = _.find([1,3,4,5,6],function(num){ return num % 2 == 0; });" );
lines.push( _.find( [ 1,6 ],function( num ) { return num % 2 == 0; }) );

lines.push( "_.sortBy([1,function(num){ return Math.sin(num); });" );
lines.push( _.sortBy( [ 1,function( num ) { return Math.sin( num ); }) );

lines.push( "_.indexOf([1,2);" );
lines.push( _.indexOf([1,2) );

this.setData( {
text: lines.join( '\n' )
})
}
})

总结

以上就是微信小程序使用第三方库Underscore.js的全部内容，希望对大家的学习或者工作带来一定的帮助，如果有疑问大家可以留言交流。

原文地址：https://www.jb51.cc/weapp/45546.html