Mastering TypeScript/

...

/

The no Compiler Options

The no Compiler Options

Learn about several compiler options that are prefixed with the word no, and understand their functionality.

We'll cover the following...

There are also a number of compiler options that are prefixed with the word no. These options are similar to the strict options in that they further guard our code against things like unused parameters, implicit returns, and implicit any.

In this lesson, we will take a look at these compiler options and how they can detect potential errors within our code. These parameters are similar in nature to strict parameters in that they can be turned on or off and can be introduced into a code base gradually.

Note: If the strict compiler option has been set to true, then all of these options will be enabled as well.

The noImplicitAny option

When a type has not been specified for a property, parameter, or function return type, the TypeScript compiler will automatically assume that it is of type any. In strict mode, this will generate an error.

Consider the following code:

index.ts
tsconfig.json
declare function testImplicityAny();
Function returning an error due to no set return type

Here, we have a function declaration named testImplicitAny, which will generate an error. What this error indicates is that the testImplicitAny function has not specified a return type and, therefore, will return a type of any.

This can be fixed by specifying a return type as follows:

declare function testImplicityAny(): void;

Here, we specify that the testImplicityAny function returns a type of void, and the error is removed.

If a function parameter or a class property has not specified a type, then similar errors are generated.

Consider the following code:

index.ts
tsconfig.json
function testNoParamType(value) { }
class TestAny {
    id;
}
Function and class without any type declaration

Here, we have a function named testNoParamType that has a single parameter named value. The value parameter does not have a type specified. We also have a class named TestAny that has a single property named id and also does not have a type specified.

This code will produce two errors.

When we run the code, we can see that the compiler is identifying both the value parameter and the id property as implicitly being of type any.

These errors can be fixed by specifying a type in each of these cases:

index.ts
tsconfig.json
function testNoParamType(value: string) { }
class TestAny {
    id : any;
}
Function and class with types specified

Here, we modify the function signature of the testNoParamType function to type ...