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TypeScript - check if array is empty or does not exist
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In this article, we're going to have a look at how to check if the array is empty or does not exist in TypeScript code.
Quick solution:
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// for not declared array variable2
const notExists: boolean = (typeof myArray === 'undefined' || myArray.length == 0);3
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// for declared but not defined array variable5
const notExists: boolean = (myArray == null || myArray.length == 0);
In this section two approaches were presented: when the variable is not defined and when is defined but with null or undefined value.
Note: using
typeofoperator we are able to check if variable exists and is defined - this operator checks if varialbe exists.
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const array1: any[] = [];2
const array2: number[] = [1, 2, 3];3
//const array3; // not declared and not defined4
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console.log(typeof array1 === 'undefined' || array1.length == 0); // true6
console.log(typeof array2 === 'undefined' || array2.length == 0); // false7
//console.log(typeof array3 === 'undefined' || array3.length == 0); // falseOutput:
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true2
falseThe approach presented in this section is based on the fact the variables were declared. Using variable == null comparison we are able to test both conditions at the same time: value is null or undefined
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const array1: any[] = [];2
const array2: number[] = [1, 2, 3];3
// const array3; // declared but not defined4
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console.log(array1 == null || array1.length == 0); // true6
console.log(array2 == null || array2.length == 0); // false7
// console.log(array3 == null || array3.length == 0); // falseOutput:
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true2
false