你永远都不能设置一个undefined的变量,应该使用null来代替,否则你将搞混淆一个未初始化的变量和一个你设置为null的变量之间的区别。 It is useful to have two different types of "no value assigned", because you can tell the difference between a variable that is just currently without a value, and o...
而null是代表了缺失对象引用。js是不能给null设置变量或者对象属性的。一些原生方法像String.prototype.match()会返回null来表示缺失对象,看一下下面这个例子: letarray =null; array;// => nullletmovie = {name:'Starship Troopers',musicBy:null}; movie.musicBy;// => null'abc'.match(/[0-9]/);//...
在 JS 中，凡是不用的变量，JS 会定期清理掉。当我们把一个对象设置为 null 时，其实也就等于把这个对象标记为不用了，可以垃圾回收了。参考 http://www.ruanyifeng.com/blog/2014/03/undefined-vs-null.htmlhttp://stackoverflow.com/questions/5076944/what-is-the-difference-between-null-and-undefined-in-...
【摘要】 在JavaScript/TypeScript项目中,`undefined`和`null`的值都表示无,`undefined`表示不存在定义,`null`表示定义为空值的一个值;空字符串`''/""`则表示是一个长度为0的字符串。 在JavaScript/TypeScript项目中,undefined和null的值都表示无,undefined表示不存在定义,null表示定义为空值的一个值;空字符串'...
I know very well that null and undefined are distinct in JavaScript. However, I can't seem to decide whether or not use that fact when my own functions are passed one of those as its argument. Or, expressed in a different way, should myFoo(undefined) return the same thing as my...
It is quite common to confuse null and undefined, but there is an important difference between them. null Simply put, null is a JavaScript keyword that indicates the absence of a value. Surprisingly, if you run the following in your firebug console: console.log( typeof null ), you will ...
varmyNullVar =null;//null myUndefinedVar == myNullVar;//true - which not correct as both are different myUndefinedVar === myNullVar;//false - correct behavior 3.2.nullevaluates to zero One major difference betweennullandundefinedis in the way they are converted to primitive types. ...
总而言之,undefined 是一个意料之外的空值,null 是一个意料之中的空值。 参考: http://www.ruanyifeng.com/blog/2014/03/undefined-vs-null.html http://blog.csdn.net/leadzen/article/details/3899392 http://stackoverflow.com/questions/5101948/javascript-checking-for-null-vs-undefined-and-difference-betw...
Q: What is the difference betweennullandundefinedwhen working with arrays? A: When you create an array with empty slots, the empty slots will have the valueundefined. However, you can also explicitly set an array element tonullif you want to represent an empty value: ...
varmyNullVar =null;//null myUndefinedVar == myNullVar;//true - which not correct as both are different myUndefinedVar === myNullVar;//false - correct behavior 3.2.nullevaluates to zero One major difference betweennullandundefinedis in the way they are converted to primitive types. ...