实现接口和对象(Implementing Interfaces and Objects)

 正如你刚才提到的，es5-shim在浏览器的JavaScript引擎不兼容ES5的情况下增加了一些JavaScript函数，比如map，reduce，some和forEach。 Underscore.js在“_”命名空间中添加了类似于上述（和更多）的实用程序方法。 所以，在这种情况下，在同一个应用程序中使用这两个都是多余的。 
 
 也就是说，es5-shim增加了一些功能，比如Date.now，Date.toJSON，Function.bind，String.trim（以及更多），它们在Underscore.js中没有直接的等价物。 例如Underscore提供的_.bind和_.bindAll等同于Function.bind，但Underscore.js不提供Date.now和Date.toJSON。 
 
 因此，如果您使用es5-shim提供的其他方法，则可以在应用程序中使用es5-shim和Underscore.js。 但是，如果您不使用这些额外的方法，那么使用es5-shim只会是应用程序大小的不必要的增加和带宽的浪费。 

es5-shim, as you rightly mentioned, adds some JavaScript functions like map, reduce, some and forEach on Array if the browser's JavaScript engine is not ES5 compatible. Underscore.js adds utility methods similar to the above (and more) within the "_" namespace. So, in this case, using both in the same application is redundant. 
 
That said, es5-shim, adds a few more functions like Date.now, Date.toJSON, Function.bind, String.trim (and more) some which don't have direct equivalents in Underscore.js. For example Underscore does provide _.bind and _.bindAll that is equivalent to Function.bind, but Underscore.js does not provide Date.now and Date.toJSON. 
 
So, if you use these additional methods provided by es5-shim you can stay with both es5-shim and Underscore.js in your application. But, if you are not using these additional methods, then using es5-shim would just be an unnecessary increase in application size and waste of bandwidth.