Variable used before definition JS-0129
Bug risk
Major
a year ago
—
2 years old
'files' was used before it was defined.
100 formdata.append("receiver",currentChannel)
101 formdata.append("pid",posting_id)
102 for(let i in files) {
103 formdata.append("file_"+i,files[i])104 }
105 files = []
106 getById("filesDiv").innerHTML=""'files' was used before it was defined.
99 formdata.append("reply_id",reply_id)
100 formdata.append("receiver",currentChannel)
101 formdata.append("pid",posting_id)
102 for(let i in files) {103 formdata.append("file_"+i,files[i])
104 }
105 files = []'files' was used before it was defined.
102 for(let i in files) {
103 formdata.append("file_"+i,files[i])
104 }
105 files = []106 getById("filesDiv").innerHTML=""
107
108 fetch("/api/post", {
Description
It is recommended to use a variable only after it is defined as it might produce errors at runtime.
In JavaScript, prior to ES6, variable and function declarations are hoisted to the top of a scope, so it's possible to use identifiers before their formal declarations in code. This can be confusing and some believe it is best to always declare variables and functions before using them.
In ES6, block-level bindings (let and const) introduce a "temporal dead zone" where a ReferenceError will be thrown with any attempt to access the variable before its declaration.
Bad Practice
alert(a);
var a = 10;
f();
function f() {}
function g() {
return b;
}
var b = 1;
{
alert(c);
let c = 1;
}
Recommended
var a;
a = 10;
alert(a);
function f() {}
f(1);
var b = 1;
function g() {
return b;
}
{
let c;
c++;
}