'number'/'string'/'boolen'/'undefined'/'object'/'function' [特例]typeof null=>'object'确实属于基本类型值,但null代表空对象指针(没有指向任何的内存空间),可以理解为typeof的bug typeof检测数/正则/对象,最后返回的都是'object',也就是基于这种方式无法细分对象 1. 2. 3. 4. 5. 6. 7. 面试题 ...
varexp=null;if(typeofexp=="null"){alert("is null");} 为了向下兼容,exp 为 null 时,typeof null 总返回 object,所以不能这样判断。 代码如下: 代码语言:javascript 代码运行次数:0 复制 Cloud Studio代码运行 varexp=null;if(isNull(exp)){alert("is null");} 判断字符串是否为空 s 匹配任何空白...
"string" --- 如果这个值是字符串。 "number" --- 如果这个值是数值。 "object" --- 如果这个值是对象或者null; "function" --- 如果这个值是函数。 */letstr ='str';alert(typeofabc);//undefined;alert(typeofundefined);//undefinedalert(typeofcheck(str));//undefinedalert(typeof'');//string...
所以 s 可能并不是字符串类型,如果 s 是 undefined 或者 null,也认为是空的话,那么s == ''并不成立,得出错误的判断...null == undefiend // true null === undefined // false 所以上面判断字符串是否为空串可以简写为: function isEmptyStr(s) {...判断字符串是否为空可能会有人从相反的角度出发,...
// TypeError: Cannot covert undefined or null ot objectgoodEmptyCheck(undefined) goodEmptyCheck(null)复制代码 1. 2. 2.4 针对 null 和 undefined,改良检查空对象方法 如果你不想它抛出 TypeError 的异常,你可以添加一个额外的检查。 let value;
The method takes a URL string, as well as a few options which you should pass through unmodified if calling super.fetch(). It must return a promise for a Node.js Buffer object, or return null if the resource is intentionally not to be loaded. In general, most cases will want to ...
attr('action', null) //=> remove attribute // multiple attributes: form.attr({ action: '/create', method: 'post' })before before(content) ⇒ self Add content to the DOM before each element in the collection. The content can be an HTML string, a DOM node or an array of nodes...
The signature of WebGLRenderer.copyFramebufferToTexture() has changed. It is now copyFramebufferToTexture( texture, position = null, level = 0 ). For more information, check out the example webgl_framebuffer_texture.163 → r164LWOLoader uses a new conversion from left to right-handed coordi...
For a ready-to-run sample app using streams, check out this example onGitHub. Stream considerations Userequest.bodyto obtain the maximum benefit from using streams. You can still continue to use methods likerequest.text(), which always return the body as a string. ...
Node REPL supports multiline expression similar to JavaScript. Let's check the following do-while loop in action −$ node > var x = 0 undefined > do { ... x++; ... console.log("x: " + x); ... } while ( x < 5 ); x: 1 x: 2 x: 3 x: 4 x: 5 undefined > ...