Why do the following two writing methods produce two different results? Ask the boss for a detailed answer. Personally, I think it is related to the block-level scope of function parameters. But it"s still weird to understand, and it"s weird to look at it with chrome debugger. Why is the last input x output based on Block? Thank you very much ~
function test (x, y = function t () { x = 2 }) {
// var x
y()
console.log(x) // 2
}
debugger
test()If default value parameter initializers exist, a second Environment Record is created for the body declarations.
if there is a function default value, a second environment record is created for the function body, which is below the function default value.
is similar to:
- in the first case, var x overrides the parameter variable x;
The second case of - is simple: when test () is called, no y is passed, and a closure is formed. The y function can still access the local variable x and even modify it.
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