代码语言:txt 复制 function setGlobalVariable() { globalVariable = "Hello, world!"; } setGlobalVariable(); 在上述代码中,没有使用var、let或const关键字声明globalVariable变量,因此它将成为全局变量。 需要注意的是,为了避免意外地创建全局变量,建议始终使用var、let或const关键字声明变量。 全局变量的优势在于...
函数是 JavaScript 中的基本组件之一。JavaScript 中的函数类似于过程——一组执行任务或计算值的语句。但要成为函数,这个过程应该接受输入并返回与输入存在某些明显关系的输出。要使用一个函数,你必须将其定义在你希望调用它的作用域内。
// here we are in global scope var globalVariable = 'xyz'; function f() { var localVariable = true; function g() { var anotherLocalVariable = 123; // All variables of surround scopes are accessible localVariable = false; globalVariable = 'abc'; } } // here we are again in global...
Prior to ES6, function declarations were only allowed at the top level within a JavaScript file or within another function. While some implementations bent the rule, it was not technically legal to define functions inside the body of loops, conditionals, or other blocks. In the strict mode of ...
Regular expressions and the RegExp class, which define textual patterns and are useful for text processing. This section also covers regular expression syntax in detail. The Date class for representing and manipulating dates and times. The Error class and its various subclasses, instances of which ...
myname = "global"; // global variable function func() { var myname; // same as -> var myname = undefined; alert(myname); // "undefined" myname = "local"; alert(myname); // "local" } func(); 这里有必要对“变量提前”作进一步补充,实际上从JavaScript引擎的工作机制上看,这个过程...
For example, JavaScript doesn't throw an error when you use a misspelled variable, and instead creates a new global one. When you start learning JavaScript, having fewer errors is convenient. However, it can lead to writing code that is harder for browsers to optimize and harder for you to...
varmap;//Global variablerequire(["esri/map"],function(Map) { map =newMap("myMap", {basemap:"national-geographic"}); }); }); 这意味着我们可以在浏览器控制台中访问地图的属性。在缩放地图和所需的范围作为地图初始范围之后,使用Ctrl+Shift+I命令(在 Chrome 中)打开开发者工具。在 JavaScript ...
Consider a "single var" pattern. Define all variables needed in your function at the very top of the function so you have a single place to look for variables and hopefully prevent accidental globals. Variable hoisting Here's an interesting example that shows an important aspect of local versus...
-d, --define <expr>[=value] Global definitions. --ecma <version> Specify ECMAScript release: 5, 2015, 2016, etc. -e, --enclose [arg[:value]] Embed output in a big function with configurable arguments and values. --ie8 Support non-standard Internet Explorer 8. Equivalent to setting ...