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Aprenda Null vs Undefined | Data Types and Variables
Introduction to JavaScript

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Null vs Undefined

Similarities Between null and undefined

  • Both are Falsy:
    A falsy (sometimes written falsey) value is a value that is considered as false when encountered in a Boolean context. There are six-falsy-value in JavaScript.

    • NaN (Not A Number)

    • 0 (Zero)

    • null

    • undefined

    • '' (empty string)

    • false
      Any value other than the above six falsy values, in JavaScript, will be considered as truthy.

  • Both are Primitive Values:
    JavaScript has seven primitive values including null and undefined . Here is a full list:

    • Null

    • Undefined

    • String

    • Number

    • BigInt

    • Symbol

    • Boolean

null !== undefined:

Although null and undefined share some similarities but they are different from each other and it is obvious that the null and undefined are not strictly equal.

1
console.log(null === undefined);
copy

But null loosely equals undefined.

1
console.log(null == undefined)
copy

As we talk in the previous chapter == checks the loose equality. But In JavaScript, a double equals tests for loose equality and it performs type coercion. type coercion means converting the value to the common type. But === does not perform type type coercion.

Summary:

  • The undefined variables are those variables that are declared without any values assigned to them.

  • null is not assigned to a variable by default like the undefined .

  • Both the null and undefined are falsy values.

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Seção 3. Capítulo 32

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book
Null vs Undefined

Similarities Between null and undefined

  • Both are Falsy:
    A falsy (sometimes written falsey) value is a value that is considered as false when encountered in a Boolean context. There are six-falsy-value in JavaScript.

    • NaN (Not A Number)

    • 0 (Zero)

    • null

    • undefined

    • '' (empty string)

    • false
      Any value other than the above six falsy values, in JavaScript, will be considered as truthy.

  • Both are Primitive Values:
    JavaScript has seven primitive values including null and undefined . Here is a full list:

    • Null

    • Undefined

    • String

    • Number

    • BigInt

    • Symbol

    • Boolean

null !== undefined:

Although null and undefined share some similarities but they are different from each other and it is obvious that the null and undefined are not strictly equal.

1
console.log(null === undefined);
copy

But null loosely equals undefined.

1
console.log(null == undefined)
copy

As we talk in the previous chapter == checks the loose equality. But In JavaScript, a double equals tests for loose equality and it performs type coercion. type coercion means converting the value to the common type. But === does not perform type type coercion.

Summary:

  • The undefined variables are those variables that are declared without any values assigned to them.

  • null is not assigned to a variable by default like the undefined .

  • Both the null and undefined are falsy values.

Switch to desktopMude para o desktop para praticar no mundo realContinue de onde você está usando uma das opções abaixo
Tudo estava claro?

Como podemos melhorá-lo?

Obrigado pelo seu feedback!

Seção 3. Capítulo 32
Switch to desktopMude para o desktop para praticar no mundo realContinue de onde você está usando uma das opções abaixo
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