![]() ( 'question' in obj & obj. However, typeof x may still throw an error if you later declare x using let or const: typeof x // Throws "ReferenceError: Cannot access 'x' before initialization" because of `let` let x = 42 Checking Whether Object Properties are UndefinedĬhecking whether an object property is undefined is subtle, because if you accessĪ property that doesn't exist in the object, JavaScript will report the property's value as undefined x = undefined // Throws a ReferenceError typeof x = 'undefined' // true Or not, you should use typeof x = 'undefined'. Strictly equal to undefined regardless of whether is has been declared When using x = undefined, JavaScript checks if x is a declared variable Theīiggest difference between these two approaches is that, if x has not been declared, x = undefined throws X = undefined & typeof x = 'undefined' // trueĪnother alternative is checking if typeof x = 'undefined'. Make sure you use strict equality = to check if a value is This article is a good starting point for the same, however, we do emphasize more on the JavaScript not equal ( & ) operators. Use the JavaScript ternary operator ( ?:)to make the code more concise.In JavaScript, checking if a variable is undefined can be a bit tricky sinceĪ null variable can pass a check for undefined if not written properly.Īs a result, this allows for undefined values to slip through and vice versa.If the logic contains many if.else statements, you should avoid using the ternary operators. It’s a good practice to use the ternary operator when it makes the code easier to read. Output: Fast Code language: JavaScript ( javascript ) Let message = speed >= 120 ? 'Too Fast' : speed >= 80 ? 'Fast' : 'OK' The following example shows how to use two ternary operators in the same expression: let speed = 90 Let canChange = locked != 1 Code language: JavaScript ( javascript ) 3) Using multiple JavaScript ternary operators example ![]() In this case, you can simplify it by using a Boolean expression as follows: let locked = 1 If the locked is 1, then the canChange variable is set to false, otherwise, it is set to true. Let canChange = locked != 1 ? true : false Code language: JavaScript ( javascript ) See the following example: let locked = 1 In this example, the returned value of the ternary operator is the last value in the comma-separated list. redirect to nextURL here console.log(nextURL) // '/admin' Code language: JavaScript ( javascript ) ? (alert( 'You will redirect to admin area'), '/admin') The following example uses the ternary operator to perform multiple operations, where each operation is separated by a comma. 1) Using the JavaScript ternary operator to perform multiple statements Let’s take some examples of using the ternary operator. However, the or Strict inequality operator does not attempt to do so and returns false if the values are unequal or of. This operator tries to compare values irrespective of whether they are of different types. In this syntax, if the condition is true, the variableName will take the result of the first expression ( expressionIfTrue) or expressionIfFalse otherwise. The JavaScript not equal or inequality operator () checks whether two values are not equal and returns a boolean value. The following shows the syntax of the ternary operator used in an expression: let variableName = condition ? expressionIfTrue : expressionIfFalse Code language: JavaScript ( javascript ) If it is false, the second expression ( expressionIfFalse) executes. If the condition is true, the first expression ( expresionIfTrue) executes. In this syntax, the condition is an expression that evaluates to a Boolean value, either true or false. ![]() Here’s the syntax of the ternary operator: condition ? expressionIfTrue : expressionIfFalse Code language: JavaScript ( javascript ) Message = age >= 16 ? 'You can drive.' : 'You cannot drive.' ![]() Or you can use the ternary operator in an expression as follows: let age = 18 Alternatively, you can use a ternary operator instead of the if-else statement like this: let age = 18 Īge >= 16 ? (message = 'You can drive.') : (message = 'You cannot drive.') In this example, we show a message that a person can drive if the age is greater than or equal to 16. For example: let age = 18 Ĭonsole.log(message) Code language: JavaScript ( javascript ) When you want to execute a block if a condition evaluates to true, you often use an if…else statement. Introduction to JavaScript ternary operator Summary : in this tutorial, you will learn how to use the JavaScript ternary operator to make your code more concise. ![]()
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