With Javascript, we have the flexibility to push values that we want to variables easily. However, in TypeScript, how can we block (throw an error) this action?
let array: Array<string> = [];
array.push(5);
console.log(array);
Even though my IDE notifies me that 5 is not a string, the code still compiles and displays the array with the value 5. How can I prevent this? I want my program to halt the operation of pushing 5 to the array.
What a thought-provoking inquiry! Before considering runtime validation, it's worth questioning the necessity if compile-time prevention is already ensuring type safety within your TypeScript coded environment.
If needed, implementing a simple check can be done as follows:
function validateAndPush(array: Array<string>, value: string): void {
if (typeof value !== 'string') {
throw new TypeError('The value must be of type string!')
}
array.push(value)
}
let myArray: Array<string> = []
validateAndPush(myArray, 'hello') // This will work
validateAndPush(myArray, 123) // This will fail at both compile and runtime
There are various libraries available to assist with such validations, commonly referred to as "runtime type assertions." For instance, you may explore tools like is, izzy, or @sindresorhus/is.
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