When you need to find the length of a JavaScript string, you can use the .length property, which is available for any JavaScript string you have in your code.
The following .length property value returns 11 because the string is 11 characters long:
let str = "Hello World";
console.log(str.length); // 11
You can even use it directly to any string you encounter:
console.log("My name is Jack".length); // 15
This is because JavaScript automatically converts string primitives to String objects (with capital “S”), so you can call String object methods on it directly.
The .length property will return 0 for empty strings:
console.log("".length); // 0
A JavaScript Array also has the .length property that returns how many elements the Array contains:
console.log([1, 2].length); // 2
To avoid type mismatch between an Array and a String, you can check the data type of your variable with typeof operator before you get its length.
The following example assumes that the variable res is a response from a web API call. You don’t know its type, so you check it with typeof :
if(typeof res === "string"){
console.log(`The length of res variable is: ${res.length} characters`);
} else {
console.log("Variable res is not a string!");
}
See also: Checking types with JavaScript typeof
