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JavaScript

Posted by SeHyun Choi
SeHyun Choi
3,441 Points

What is difference between var message; and var message ="";

What is the difference between 

var message;

and

var message ="";

Aren't they the same? Aren't they all empty variable called message?

When I do var message; Then my code doesn't loop but when i do var message =""; Then it correctly loops. What is the difference?

CODE

var students = [

    {
        name : "Sarah",

        age : 26,

        country : "USA"

    },


    {
        name : "Sammy",

        age : 23,

        country : "USA"

    },


    {
        name : "Yohan",

        age : 46,

        country : "USA"

    },



];

var student;
var message ="";


function print(message) {
    var printIt = document.write(message);
    return printIt;
}   


for(var i = 0; i < students.length; i += 1) {

    student = students[i];

    message += "<h2>Student: " + student.name + "</h2>";
    message += "<p>Age: " + student.age + "</p>";
    message += "<p>Country: " + student.country + "</p>";

}

print(message);

1 Answer

Steven Parker
Steven Parker
243,160 Points
Steven Parker
Steven Parker
243,160 Points

When you write just "var message;" you declare the variable as existing, but it has no contents yet. When you add the ="" to it, you are putting a string into it. The string happens to be empty itself, but it's still a string and the variable contents are no longer undefined.

The "+=" operator is a special kind of assignment that adds onto the contents a variable already has. So it works fine with a variable that starts with an empty string in it, but not with one that is still undefined.

SeHyun Choi
SeHyun Choi
3,441 Points

Thank you.