We then use "if not" (!) to check if the player has entered a valid choice. If choice is null, undefined, or an empty string, the condition inside the first if statement is true, and the code inside the block is executed. Therefore, the output to the console is "You didn't ...
“Function declarations should not be placed in blocks. Use a function expression or move the statement to the top of the outer function.”:“函数的声明不能放在类似if的块中,需要放在外部函数的顶部.” 针对自己项目中遇到的一些提示,做一些举例说明: 1 [W099]:Mixed spaces and tabs 这个错误是最常...
conststring = 'string';!!string; // true Boolean(string); // true 数值 constnumber = 100;!!number; // true Boolean(number); // true 虚值 在JavaScript中，有6个虚值。如果将其中任何一个字符串转换为Boolean，它将变为false 。false undefined null NaN "" (empty string)任何不为虚值的都会转换...
// then run the following block.if (!argument) { return 'The argument is empty'} else { return 'The argument is not empty'} // Let's convert the previous block to a positive check const argument = null if (argument) { return 'The argument is present'} else { return 'The argument...
if(!!username){ console.log("Username is defined and not empty."); }else{ console.log("Username is undefined or empty."); } 在这个例子中,!!username用于检查username是否有值。如果username有值(非空字符串),条件成立,输出"Username is defined and not empty.";否则,输出"Username is undefined or...
functiontoUppercase(string){if(typeofstring!=="string"){throwTypeError("Wrong type given, expected a string");}returnstring.toUpperCase();}toUppercase(4); 如果你在浏览器或 Node.js 中运行此代码,程序将停止并报告错误: 代码语言:javascript
2. 简化 if true...else 对于不包含大逻辑的 if-else 条件,可以使用下面的快捷写法。我们可以简单地使用三元运算符来实现这种简化。 如果有嵌套的条件,可以这么做。 3. if 判断值是否存在 这是我们都在使用的一种常用的简便技巧,在这里仍然值得再提一下。
If you guess that theconsole.log()call would either outputundefinedor throw an error, you guessed incorrectly. Believe it or not, it will output10. Why? In most other languages, the code above would lead to an error because the “life” (i.e., scope) of the variableiwould be restrict...
map(num => { if (typeof num === "number") return; return num * 2; }); A: [] B: [null, null, null] C: [undefined, undefined, undefined] D: [ 3 x empty ] 答案: C 对数组进行映射的时候,num就是当前循环到的元素. 在这个例子中,所有的映射都是number类型,所以if中的判断typeof...
The implemented interface. If you cannot find the method you require, please let us know, and we will add it! Localized output will of course vary based on the locale and date library used. Inline examples here are based on usingmomentwith theen-USlocale. ...