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# Chapter 7. Built-in Improvements in ES6

Thus far in the book, we’ve discussed entirely new language syntax, such as property value shorthands, arrow functions, destructuring, or generators; and entirely new built-ins, such as `WeakMap`, `Proxy`, or `Symbol`. This chapter, on the other hand, is mostly devoted to existing built-ins that were improved in ES6. These improvements consist mostly of new instance methods, properties, and utility methods.

# 7.1 Numbers

ES6 introduces numeric literal representations for binary and octal numbers.

## 7.1.1 Binary and Octal Literals

Before ES6, your best bet when it comes to binary representation of integers was to just pass them to `parseInt` with a radix of `2`.

````parseInt``(``'101'``,` `2``)`
`// <- 5````

You can now use the new `0b` prefix to represent binary integer literals. You could also use the `0B` prefix, with a capital `B`. The two notations are equivalent.

````console``.``log``(``0b000``)` `// <- 0`
`console``.``log``(``0b001``)` `// <- 1`
`console``.``log``(``0b010``)` `// <- 2`
`console``.``log``(``0b011``)` `// <- 3`
`console``.``log``(``0b100``)` `// <- 4`
`console``.``log``(``0b101``)` `// <- 5`
`console``.``log``(``0b110``)` `// <- 6`
`console``.``log``(``0b111``)` `// <- 7````

In ES3, `parseInt` interpreted strings of digits starting with a `0` as an octal value. That meant things got weird quickly when you forgot to specify a radix of `10`. As a result, specifying the radix of `10` became a best practice, so that user input like `012` wouldn’t unexpectedly be parsed as the integer `10`.

````console``.``log``(``parseInt``(``'01'``))`
`// <- 1`
`console``.``log``(``parseInt``(``'012'``))`
`// <- 10`
`console``.``log``(``parseInt``(````

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