Constraining Generics
Learn how to constrain TypeScript generics.
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Let’s learn one more concept before we begin to leverage TypeScript in our polymorphic component solution.
Getting started
Let’s consider a variant of the echo function. We’ll call this echoLength.
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const echoLength = <Value> (v: Value) => {console.log(v.length);return v.length;};
Instead of echoing the input value v, the function echoes the length of the input value, i.e., v.length.
If we wrote this code out as is, the TypeScript compiler would give us an error.
index.ts(2,19): error TS2339: Property 'length' does not exist on type 'Value'.
The wrong property access error
This is an important error to pay attention to. The ...