JavaScript - Short-Circuiting

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In JavaScript, short-circuiting is a feature that checks conditions and stops as soon as it knows the answer. It doesn't look for the rest of the expression, and that prevent unnecessary evaluations.

Short-Circuiting for && operator

Short circuit evaluation with &&(AND) logical operator means if the first expression evaluates to false then whole expression will be false and the rest of the expressions will not be evaluated.

Code-snippet

Below is an example snippet of short-circuiting with the && operator.

 let x = 0 && "hello"; // x will be 0, as 0 is falsy and short-circuits let y = true && "world"; // y will be "world" because the first value is truthy let z = "hello" && "world"; // z will be "world" because both values are truthy console.log(x); // 0 console.log(y); // world console.log(z); // world 

Output

Following is the output of the above code

 0 world world 

Short-Circuiting for || operator

Short circuit evaluation with ||(OR) logical operator means if the first expression evaluates to true then whole expression will be true and the rest of the expressions will not be evaluated.

Code-snippet

Below is an example snippet of short-circuiting with the || operator.

 let x = 0 || "hello"; // x will be "hello" because 0 is falsy let y = true || "world"; // y will be true because the first value is truthy let z = "hello" || "world"; // z will be "hello" because the first value is truthy console.log(x); // hello console.log(y); // true console.log(z); // hello 

Output

Following is the output of the above code

 hello true hello 

Short-Circuiting Assignment

Short-circuiting can be used in assignment operations as well. Means, if you have to assign something based on a condition, you can use short-circuiting.

Code-snippet

Below is an example snippet of short-circuiting in assignment operations.

 let x = 0; let y = 10; let z = x || y; // z will be 10 because x is falsy console.log(z); // 10 

In above example, z will be assigned the value of y because x is falsy.

Output

Following is the output of the above code

 10 

Short-Circuiting in Function Calls

Short-circuiting can be used in function calls as well. Means, if you have to call a function based on a condition, you can use short-circuiting.

Code-snippet

Below is an example snippet of short-circuiting in function calls.

 function greet(name) { return name || "Guest"; } let x = greet("John"); // x will be "John" because name is truthy let y = greet(""); // y will be "Guest" because name is falsy console.log(x); // John console.log(y); // Guest 

In above example, if name is truthy, it will return the name, otherwise it will return "Guest".

Output

Following is the output of the above code

 John Guest