> For the complete documentation index, see [llms.txt](https://jorgedacostaza.gitbook.io/typescript-pt/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jorgedacostaza.gitbook.io/typescript-pt/recap/equality.md).

# Igualdade

## Equality

One thing to be careful about in JavaScript is the difference between `==` and `===`. As JavaScript tries to be resilient against programming errors `==` tries to do type coercion between two variables e.g. converts a string to a number so that you can compare with a number as shown below:

```javascript
console.log(5 == "5"); // true   , TS Error
console.log(5 === "5"); // false , TS Error
```

However, the choices JavaScript makes are not always ideal. For example, in the below example the first statement is false because `""` and `"0"` are both strings and are clearly not equal. However, in the second case both `0` and the empty string (`""`) are falsy (i.e. behave like `false`) and are therefore equal with respect to `==`. Both statements are false when you use `===`.

```javascript
console.log("" == "0"); // false
console.log(0 == ""); // true

console.log("" === "0"); // false
console.log(0 === ""); // false
```

> Note that `string == number` and `string === number` are both compile time errors in TypeScript, so you don't normally need to worry about this.

Similar to `==` vs. `===`, there is `!=` vs. `!==`

So ProTip: Always use `===` and `!==` except for null checks, which we cover later.

## Structural Equality

If you want to compare two objects for structural equality `==`/`===` are ***not*** sufficient. e.g.

```javascript
console.log({a:123} == {a:123}); // False
console.log({a:123} === {a:123}); // False
```

To do such checks use the [deep-equal](https://www.npmjs.com/package/deep-equal) npm package e.g.

```javascript
import * as deepEqual from "deep-equal";

console.log(deepEqual({a:123},{a:123})); // True
```

However, quite commonly you don't need deep checks and all you really need is to check by some `id` e.g.

```typescript
type IdDisplay = {
  id: string,
  display: string
}
const list: IdDisplay[] = [
  {
    id: 'foo',
    display: 'Foo Select'
  },
  {
    id: 'bar',
    display: 'Bar Select'
  },
]

const fooIndex = list.map(i => i.id).indexOf('foo');
console.log(fooIndex); // 0
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://jorgedacostaza.gitbook.io/typescript-pt/recap/equality.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.