Today #Day124 of #365DaysOfCode, Learning Essential JavaScript Interview Questions.
15. What is a “closure” in JavaScript? Provide an example.
A closure is an inner function that has access to the variables in the outer (enclosing) function’s scope chain.
The closure has access to variables in three scopes; specifically:
variable in its own scope,
variables in the enclosing function’s scope, and
global variables.
Here is an example:
var globalVar = "xyz";
(function outerFunc(outerArg) {
var outerVar = 'a';
(function innerFunc(innerArg) {
var innerVar = 'b';
console.log(
"outerArg = " + outerArg + "\n" +
"innerArg = " + innerArg + "\n" +
"outerVar = " + outerVar + "\n" +
"innerVar = " + innerVar + "\n" +
"globalVar = " + globalVar);
})(456);
})(123);
In the above example, variables from innerFunc, outerFunc, and the global namespace are all in scope in the innerFunc. The above code will therefore produce the following output:
outerArg = 123
innerArg = 456
outerVar = a
innerVar = b
globalVar = xyz
16. What would the following lines of code output to the console?
console.log("0 || 1 = "+(0 || 1));
console.log("1 || 2 = "+(1 || 2));
console.log("0 && 1 = "+(0 && 1));
console.log("1 && 2 = "+(1 && 2));
console.log("0 && 2893 = "+(0 && 2893));
console.log("1 && 2893 = "+(1 && 2893));
In JavaScript, both || and && are logical operators that return the first fully-determined “logical value” when evaluated from left to right.
Conclusion
Learned and practiced Essential JavaScript Interview Questions involving topics like JS closure and Logical Operator.
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