javascript 如何允许 object 键类型语法不包括 ir 在文字中和变量声明中？

Question

While running these statement in chrome console or inside script tag what I found is that the below syntax which I thought is invalid is working and all the varaibles were exposed globally which I understand could be due to curly braces are interpreted as block but that key: in front is what confuse me. But I am not sure why and looking for an explaination.

    foo: {
      a = 5,
      b = 6
    }

    console.log(a) output --->  5
    console.log(b) output --->  6


    foo: {
      a = 5;
      b = 6;
    }

    console.log(a) output --->  5
    console.log(b) output --->  6


    foo: {
      a: 5;
      b: 6;
    }

    console.log(a) output --->  5
    console.log(b) output --->  6

Answer 1

That's because foo: is interpreted as a label and your "ObjectLiteral" get's interpreted as block and the statements inside get executed.

Your code boils down to the following.

a = 5,
b = 6

Since you don't have any declaration like var , let , or const you're setting a global variable a and b

Answer 2

If you declare a variable by just assigning to it (without using let , const , var or as a function parameter), then it is global.

The labels do nothing because you have no loop to continue (or similar) from.

The blocks do nothing because you aren't using let or const which would scope variable to blocks.