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declarations are "hoisted" to the top of the current scope
// a variable declaration
var one;
// a variable assignment
one = "ūnus":
// variable declaration and assignment
var one = "ūnus";
// when this is written
one = "ūnus"; // variable assignment
var one; // variable declaration
// JavaScript interprets it in this order
var one; // hoisted to the top
one = "ūnus";
// only the declaration is hoisted
// not the assignment
console.log( two ); // undefined
var two = "duo";
// JavaScript hoists the declaration
var two;
console.log( two ); // undefined
two = "duo"; // assigned
applies to source files
function declaration vs. function expressions
// function declared after it's invoked
three();
function three(){
return "trēs";
}
// JavaScript interprets in this order
// declaration gets hoisted to the top of the scope
function three(){
return "trēs";
}
three(); // "trēs"
// assign anonymous function expression to variable four
four(); // "quattuor"
var four = function(){
return "quattuor";
}
// JavaScript interprets in this order
// variable declaration gets hoisted to the top of the scope
// assignment does not get hoisted
var four;
four(); // Error! four is not a function
four = function(){
return "quattuor";
}
can cause confusion, understand how JavaScript interprets
// declaration and expression
var five = function(){
return 5;
}
function five(){
return "quīnque";
}
five(); // ??
What is the result of invoking five() ?
can cause confusion, understand how JavaScript interprets
// declaration and expression
var five = function(){
return 5;
}
function five(){
return "quīnque";
}
five(); // ??
// JavaScript hoists only declarations
function five(){ // functions are hoisted first
return "quīnque";
}
var five; // hoisted to top of scope
five = function(){ // assignment in original position
return 5;
}
five(); // 5
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