What is the difference between any and any[ ]?

Question

What is the difference between any and any[ ]?

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Example 1 (working as expected)

name1: any;
name2: any[];
this.name1 = this.name2;

Answer 1

If we look at this TypeScript code:

let name1: any = "John";
let name2: any[] = ["Mary", "Sue", "Sally"];
name1 = name2;

let name3: any[] = ["Luke", "Paul", "Ringo"];
let name4: any = "Mark";
name3 = name4;

The Javascript that it compiles to is:

var name1 = "John";
var name2 = ["Mary", "Sue", "Sally"];
name1 = name2;
var name3 = ["Luke", "Paul", "Ringo"];
var name4 = "Mark";
name3 = name4;

JavaScript variables are dynamic and don't have a set type. I can imagine that this could be reported as a warning or error by the TypeScript compiler, but that does not stop the generation of the JavaScript or prevent the JavaScript from running.

So while there is no current compile errors or warnings for any/any[] assignments, any[] can still be used to inform the developer of expectations.

Note: This is not code I would ever write or suggest that any would ever use. This is just the OPs code with values and showing what the resulting JavaScript would be and that because it compiles to JavaScript, there can be no run-time errors due to type because variables have dynamic type. This is one of the reasons we choose to use TypeScript: compile time static type checking. For this reason, one would normally avoid any and any[] in favor of a class or interface that better represents the data. And in this case, string vs. string[] (or any other type) will show a compiler error.

In this example, both of the name1 = name2 and name3 = name4 are compile time errors as the variables infer the type from the assignment and their usage is type-checked in subsequent code.

let name1 = "John";
let name2 = ["Mary", "Sue", "Sally"];
name1 = name2; //Type 'string[]' is not assignable to type 'string'.

let name3 = ["Luke", "Paul", "Ringo"];
let name4 = "Mark";
name3 = name4; //Type 'string' is not assignable to type 'string[]'.