What will be the output of the following code: console.log(a); var a = 10;

In JavaScript, variable declarations using var are hoisted to the top of their scope, but the assignments are not. The code is effectively interpreted as:

var a;

console.log(a);

a = 10;

When console.log(a) runs, the variable a exists but has not yet been assigned a value, so its value is undefined. Therefore, the output will be undefined. After the console.log statement, a is assigned the value 10. This behavior demonstrates the difference between declaration hoisting and initialization.