问题
Recently, working with JavaScript in Developer Tool, I found strange feature. Chrome accepts any code between opening bracket with operator (plus, minus sign) and operator with closing brackets and executes it, like this:
I didn't find this behaviour in another browsers, just in Chrome.
Maybe it's a feature, but why and how it works, can it be problem with JavaScript engine?
回答1:
This is the way chrome evaluates your input:
with (typeof __commandLineAPI !== 'undefined' ? __commandLineAPI : { __proto__: null }) {
// your code here...
}
So once your input is }{
it becomes
with (typeof __commandLineAPI !== 'undefined' ? __commandLineAPI : { __proto__: null }) {}{} // indefined
Next input }-+{
becomes
undefined -+ {} // NaN
And so on.
回答2:
This happens because Chrome wraps the code you enter in the console in the following construction:
with (typeof __commandLineAPI !== 'undefined' ? __commandLineAPI : { __proto__: null }) {
// Your code
}
So, when you enter something like } 10 {, the code evaluates to:
with (typeof __commandLineAPI !== 'undefined' ? __commandLineAPI : { __proto__: null }) {
} 10 {
}
which is empty with block, a number, and empty structural block.
__commandLineAPI is the internal object that contains Chrome Command Line API.
来源：https://stackoverflow.com/questions/31359023/strange-behaviour-of-javascript-in-chrome-developer-tool