Javascript - Global (Object|Namespace|window)

Html script

Example of global variable definition:

• The common way is to declare a variable with the var keyword at the top of a script

var bar = "global variable declaration with the var keyword at the top of a script";
console.log(bar);

• Beware of variable leaking in the global scope as without the var keyword, the variable is declared in the global space.

function scope(){
    bar = "global variable declaration without the var keyword in a function";
    // Becareful, if you redeclare the same variable later with the var keyword, 
    // thanks to variable hoisting the below statement will placed at the top of its scope 
    // and the variable will not be considered global anymore but local
    // var bar = "local variable declaration with the var keyword in a function"; 
}
// Run the function to run the variable declaration
scope();
console.log(bar);

• The global object is also accessible via this at the top of a script. Adding a property to it will declare a global variable.

this.foo = "global object property declaration via the this keyword";
console.log(foo);

Window

In the browser, the global object is accessible via the window object

window.foo = "global object property declaration via the window object";
console.log(foo);

Devtool

With the devtool, open the console and type window.

Script

The first 10 variables of the global object:

function propertyRepresentation(o,v){
  this.variableName = v;
  this.type = typeof o[v];
  this.variableValue = o[v];
}

globalVariables = [];
counter = 0;
globalObject = this;
for (prop in globalObject) {
  globalVariables.push(new propertyRepresentation(globalObject,prop));
  counter++;   
  if (counter >= 10){
     more = { more: "... on a total of "+Object.keys(globalObject).length }
     globalVariables.push(new propertyRepresentation(more,"more"));
     break;
  }
}

console.log("The first 10 variables of the global object:");
console.table(globalVariables);