A Global variable is a variable that is declared in the global scope, making it a property of the global object. Global variables are accessible from all other (local) scopes. The global scope is a scope that contains every variable declared outside of a function (functions create their own...
executionContextObj={scopeChain:{...},variableObject:{message:undefined},this:{...}} 2. 执行阶段: 代码语言:javascript 复制 executionContextObj={scopeChain:{...},variableObject:{message:'find a frontend job in Canton!'},this:{...}} 详细的解析可以看下我之前翻译的一篇文章JS的执行上下文和环...
letglobalVariable=10;functionmyFunction(){console.log(globalVariable);// 可以访问全局变量} 局部作用域 在函数内部声明的变量拥有局部作用域,只能在函数内部访问。 functionmyFunction(){letlocalVariable=20;// 局部变量console.log(localVariable);// 可以访问局部变量}console.log(localVariable);// 错误:无法...
虽然我们写代码的时候一般不会直接接触内存管理,但是有一些注意事项可以让我们避免引起内存问题,甚至提升代码的性能。 全局变量(Global variable) 全局变量的访问速度远不及局部变量,应尽量避免定义非必要的全局变量。 在我们实际的项目开发中,难免会需要去定义一些全局变量,但是我们必须谨慎使用全局变量。 因为全局变量永远...
varx ="global";functionf() {varx ="local";console.log(x);// local}f();console.log(x);// global 在函数“f()”内部,全局“x”被本地“x”遮蔽。 变量是函数作用域的 大多数主流语言都是块作用域的:变量“存在于”最内部的周围代码块中。以下是 Java 的一个例子: ...
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 ...
当全局变量跟局部变量重名时,局部变量的scope会覆盖掉全局变量的scope,(当离开局部变量的scope后,又重回到全局变量的scope,) 而当全局变量遇上局部变量时,用window.globalVariableName来使用全局变量 */var variable = "variable in global";function show(){ ...
var str1 = "hello1"; //定义一个全局变量,实际上是一个variable str2 = "hello2"; //定义一个全局变量,实际上是在global下创建一个property window.str3 = "hello3"; //定义一个全局变量 function func(){ var str4 = "hello4"; //定义一个局部变量 ...
One of the important things to understand about function declarations is that the name of the function becomes a variable whose value is the function itself. Function declaration statements are “hoisted” to the top of the enclosing script, function, or block so that functions defined in this ...
console.log("firstName" in window); // true If a variable is initialized (assigned a value) without first being declared with the var keyword, it is automatically added to the global context and it is thus a global variable: function showAge () { ...