Why are function declarations handled differently in different browsers?
Although I couldn't find a reference to this easily in google, I'm familiar with the fact that, in javascript, global function declarations get interpreted before any code is executed. In other words, this works fine:
f();
function f() {}
However, I've noticed that chrome and firefox have different interpretations of what a global function declaration is. In particular, chrome is happy reading a function declaration that is inside an if block in the first pass, but firefox is not.
try {document.write(f);} // works in chrome
catch(e) {document.write(e.message);} // throws an error in firefox
try {document.write(g);} // works in chrome and firefox
catch(e) {document.write(e.message);}
if(true) function f() {}
function g() {}
You can try this example yourself with this fiddle. I'm using Chrome 16.0.912.75 and Firefox 9.0.1.
What is the ECMA standard for this behavior? Is there a term for this process of "lifting" function declarations above other code? Is what code gets "lifted" open to interpretation (are both browsers right)? Or is it a bug in one of them?
Function declarations are not valid in blocks. You have undefined behaviour which is undefined.
Function declarations at a top level (either global or top level within a function) are hoisted.
Function declarations inside blocks are a syntax error in strict mode
(function () {
"use strict";
if (true) {
function g() { }
}
})();
SyntaxError: In strict mode code, functions can only be declared at top level or immediately within another function.
The ECMA standard for this behavior is to throw a SyntaxError when parsing the script. Unfortunately doing that is not compatible with the web as Raynos says.
See Which JS function-declaration syntax is correct according to the standard? for some extended discussion on the issue.
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