Coercion

Question 0

Coercion:

Does 2 + “3” == “2” + 3?

Answer 0

Yes. JavaScript always favors the string when combining a string and a number.

All other math operators /, *, %, - convert the string to a number.

Question 1

Coercion:

Is 3 + true a valid expression in JavaScript?

Answer 1

Yes. It equals 4 because ‘true’ is converted to 1 by the JavaScript engine.

Question 2

Coercion:

Does 3 + 4 + “5” = 3 + “4” + 5?

Answer 2

No. Because JavaScript evaluates left to right.

33 != 345

Question 3

Coercion:

When null is converted to a number what is value?

Answer 3

This can mask errors!

Question 4

Coercion:

When undefined is converted to a number what is its value?

Answer 4

NaN.

Question 5

Coercion:

Is the statement

var x = NaN;
x == NaN;

True or false?

Answer 5

False. NaN by definition is never equal to itself.

Question 6

Coercion:

If and object has both a valueOf and a toString method defined. What should the toString return, the type of the object or the string representation of the value?

Answer 6

The string representation of the value. The avoids errors with implicit conversion.

Question 7

Coercion:

What is a simple way to avoid implicit coercion and explicitly convert a value to a number?

Answer 7

Use the + operator.

+“123” === 123
+form.date.value === today.getDate;

Question 8

Coercion:
True/False

The == operator uses implied conversion and the === does not.

Answer 8

True.

== attempts to coerce the values into similar type before comparison. It is usually preferable to use the === operator.