JavaScript Comparison and Logical Operators
Comparison and Logical operators are used to test for true or false.
Comparison Operators
Comparison operators are used in logical statements to determine equality or difference between variables or values.
Given that x = 5, the table below explains the comparison operators:
OperatorDescriptionComparingReturnsTry it==equal tox == 8falseTry it »x == 5trueTry it »x == "5"trueTry it »===equal value and equal typex === 5trueTry it »x === "5"falseTry it »!=not equalx != 8trueTry it »!==not equal value or not equal typex !== 5falseTry it »x !== "5"trueTry it »x !== 8trueTry it »>greater thanx > 8falseTry it »<less thanx < 8trueTry it »>=greater than or equal tox >= 8falseTry it »<=less than or equal tox <= 8trueTry it »
How Can it be Used
Comparison operators can be used in conditional statements to compare values and take action depending on the result:
if (age < 18) text = "Too young";
You will learn more about the use of conditional statements in the next chapter of this tutorial.
Logical Operators
Logical operators are used to determine the logic between variables or values.
Given that x = 6 and y = 3, the table below explains the logical operators:
OperatorDescriptionExampleTry it&&and(x < 10 && y > 1) is trueTry it »||or(x == 5 || y == 5) is falseTry it »!not!(x == y) is trueTry it »
Conditional (Ternary) Operator
JavaScript also contains a conditional operator that assigns a value to a variable based on some condition.
Syntax
variablename = (condition) ? value1:value2
Example
var voteable = (age < 18) ? "Too young":"Old enough";
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If the variable age is a value below 18, the value of the variable voteable will be "Too young", otherwise the value of voteable will be "Old enough".
Comparing Different Types
Comparing data of different types may give unexpected results.
When comparing a string with a number, JavaScript will convert the string to a number when doing the comparison. An empty string converts to 0. A non-numeric string converts to NaN which is always false.
CaseValueTry2 < 12trueTry it »2 < "12"trueTry it »2 < "John"falseTry it »2 > "John"falseTry it »2 == "John"falseTry it »"2" < "12"falseTry it »"2" > "12"trueTry it »"2" == "12"falseTry it »
When comparing two strings, "2" will be greater than "12", because (alphabetically) 1 is less than 2.
To secure a proper result, variables should be converted to the proper type before comparison:
age = Number(age);
if (isNaN(age)) {
voteable = "Error in input";
} else {
voteable = (age < 18) ? "Too young" : "Old enough";
}
if (isNaN(age)) {
voteable = "Error in input";
} else {
voteable = (age < 18) ? "Too young" : "Old enough";
}
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Test Yourself with Exercises!
Exercise 1 » Exercise 2 » Exercise 3 » Exercise 4 » Exercise 5 » Exercise 6 »
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