变量提升 好像只针对var声明的全局变量，let声明的就会报错

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#1 Created at ... [Delete] [Delete and Lock User]

function foo(){
    var x="a"+y;
    console.log(x);
    let y = "b";
}
foo(); //ReferenceError: Cannot access 'y' before initialization

#2 Created at ... [Delete] [Delete and Lock User]

确实是这样，我感觉var就像==一样，正在被抛弃。我用webstorm写JavaScript用var时都会提示用let和const替换。