ﺪﯿﻫﺩ ﻩﺯﺎﺟﺍ ﺖﭙﯾﺮﮑﺳﺍ ﺍﻭﺎﺟ

فهرست مطالب

نمایش فهرست مطالب

ﺪﺷ ﯽﻓﺮﻌﻣ let ﯼﺪﯿﻠﮐ ﻪﻤﻠﮐ

ﺪﻨﺘﺴﯿﻧ ﺩﺪﺠﻣ ﻥﻼﻋﺍ ﻞﺑﺎﻗ let ﺎﺑ ﻩﺪﺷ ﻒﯾﺮﻌﺗ ﯼﺎﻫﺮﯿﻐﺘﻣ

ﺪﻧﻮﺷ ﻡﻼﻋﺍ ﻩﺩﺎﻔﺘﺳﺍ ﺯﺍ ﻞﺒﻗ ﺪﯾﺎﺑ let ﺎﺑ ﻩﺪﺷ ﻒﯾﺮﻌﺗ ﯼﺎﻫﺮﯿﻐﺘﻣ

ﺪﻨﺷﺎﺑ Block Scope ﯼﺍﺭﺍﺩ let ﺎﺑ ﻩﺪﺷ ﻒﯾﺮﻌﺗ ﯼﺎﻫﺮﯿﻐﺘﻣ

ﺩﺮﮐ ﻡﻼﻋﺍ ﻩﺭﺎﺑﻭﺩ ﻥﺍﻮﺗ ﯽﻤﻧ

.ﺩﺮﮐ ﻡﻼﻋﺍ ﺍًﺩﺪﺠﻣ ﻥﺍﻮﺗ ﯽﻤﻧlet ﺎﺑ ﻩﺪﺷ ﻒﯾﺮﻌﺗ ﯼﺎﻫﺮﯿﻐﺘﻣ

.ﺪﯿﻨﮐ ﻡﻼﻋﺍ ﺍًﺩﺪﺠﻣ ﺍﺭ let ﺎﺑ ﻩﺪﺷﻡﻼﻋﺍ ﺮﯿﻐﺘﻣ ﮏﯾ ﯽﻓﺩﺎﺼﺗ ﺭﻮﻃﻪﺑ ﺪﯿﻧﺍﻮﺗﯽﻤﻧ

:ﺪﯿﻫﺩ ﻡﺎﺠﻧﺍ ﺍﺭ ﺭﺎﮐ ﻦﯾﺍ ﺪﯾﺎﺒﻧ، ﺪﯿﻫﺩ ﻩﺯﺎﺟﺍ<"code class="w3-codespan> ﺎﺑ

let x = "John Doe";

let x = 0;

:ﺪﯿﻧﺍﻮﺗ ﯽﻣ var ﺎﺑ

var x = "John Doe";

var x = 0;

`Block Scope`

.ﺩﻮﺑ Function Scope ﻭ Global Scope ﯼﺍﺭﺍﺩ ﺖﭙﯾﺮﮑﺳﺍ ﺍﻭﺎﺟ ،ES6 (2015) ﺯﺍ ﻞﺒﻗ

ES6 ﺩﺮﮐ ﯽﻓﺮﻌﻣ ﺍﺭ ﺖﭙﯾﺮﮑﺳﺍ ﺍﻭﺎﺟ ﻢﻬﻣ ﯼﺪﯿﻠﮐ ﻪﻤﻠﮐ ﻭﺩ: let ﻭ con

.ﺪﻨﻨﮐ ﯽﻣ ﻪﺋﺍﺭﺍ ﺖﭙﯾﺮﮑﺳﺍ ﺍﻭﺎﺟ ﺭﺩ ﺍﺭ Block Scope ﯼﺪﯿﻠﮐ ﻪﻤﻠﮐ ﻭﺩ ﻦﯾﺍ

ﺪﻨﺘﺴﯿﻧ ﯽﺳﺮﺘﺳﺩ ﻞﺑﺎﻗ { } ﮎﻮﻠﺑ ﮏﯾ ﺭﺩ ﻩﺪﺷ ﻡﻼﻋﺍ ﯼﺎﻫﺮﯿﻐﺘﻣ

`ﻝﺎﺜﻣ`

{ 
  let x = 2;
  }
// x can NOT be used here

.ﺪﻨﺷﺎﺑ ﻪﺘﺷﺍﺩ ﯽﮐﻮﻠﺑ ﻩﺩﻭﺪﺤﻣ ﺪﻨﻧﺍﻮﺗ ﯽﻤﻧ var ﯼﺪﯿﻠﮐ ﻪﻤﻠﮐ ﺎﺑ ﻩﺪﺷ ﻡﻼﻋﺍ ﯼﺎﻫﺮﯿﻐﺘﻣ

ﺖﺷﺍﺩ ﯽﺳﺮﺘﺳﺩ ﻥﺁ ﺯﺍ ﻥﺍﻮﺗ ﯽﻣ ﺍﺭ { } ﮎﻮﻠﺑ ﮏﯾ ﻞﺧﺍﺩ ﺭﺩ ﻩﺪﺷ ﻡﻼﻋﺍ ﯼﺎﻫﺮﯿﻐﺘﻣ

`ﻝﺎﺜﻣ`

{ 
  var x = 2; 
  }
// x CAN be used here

`ﺎﻫﺮﯿﻐﺘﻣ ﺩﺪﺠﻣ ﻡﻼﻋﺍ`

.ﺪﻨﮐ ﺩﺎﺠﯾﺍ ﯽﺗﻼﮑﺸﻣ ﺪﻧﺍﻮﺗ ﯽﻣ var ﯼﺪﯿﻠﮐ ﻪﻤﻠﮐ ﺯﺍ ﻩﺩﺎﻔﺘﺳﺍ ﺎﺑ ﺮﯿﻐﺘﻣ ﮏﯾ ﺩﺪﺠﻣ ﻡﻼﻋﺍ

ﺪﻨﮐ ﯽﻣ ﻡﻼﻋﺍ ﺍًﺩﺪﺠﻣ ﺍﺭ ﺮﯿﻐﺘﻣ ﺰﯿﻧ ﮎﻮﻠﺑ ﮏﯾ ﻞﺧﺍﺩ ﺭﺩ ﺮﯿﻐﺘﻣ ﮏﯾ ﺩﺪﺠﻣ ﻡﻼﻋﺍ

`ﻝﺎﺜﻣ`

var x = 10;
// Here x is 10

{ 
var x = 2;
// Here x is 2
}

// Here x is 2

→ ﺪﯿﻨﮐ ﻥﺎﺤﺘﻣﺍ ﺍﺭ ﻥﺁ ﻥﺎﺗﺩﻮﺧ

<!DOCTYPE html>
<html>
<body>

<h2>Redeclaring a Variable Using var</h2>

<p id="demo"></p>

<script>
var  x = 10;
// Here x is 10

{  
var x = 2;
// Here x is 2
}

// Here x is 2
document.getElementById("demo").innerHTML = x;
</script>

</body>
</html>

.ﺪﻨﮐ ﻞﺣ ﺍﺭ ﻞﮑﺸﻣ ﻦﯾﺍ ﺪﻧﺍﻮﺗ ﯽﻣ let ﯼﺪﯿﻠﮐ ﻪﻤﻠﮐ ﺯﺍ ﻩﺩﺎﻔﺘﺳﺍ ﺎﺑ ﺮﯿﻐﺘﻣ ﮏﯾ ﺩﺪﺠﻣ ﻡﻼﻋﺍ

ﺪﻨﮐ ﯽﻤﻧ ﻡﻼﻋﺍ ﺍًﺩﺪﺠﻣ ﺍﺭ ﻥﺁ ﺯﺍ ﺝﺭﺎﺧ ﺮﯿﻐﺘﻣ ،ﮎﻮﻠﺑ ﮏﯾ ﻞﺧﺍﺩ ﺭﺩ ﺮﯿﻐﺘﻣ ﮏﯾ ﺩﺪﺠﻣ ﻡﻼﻋﺍ

`ﻝﺎﺜﻣ`

let x = 10;
// Here x is 10

{
let x = 2;
// Here x is 2
}

// Here x is 10

→ ﺪﯿﻨﮐ ﻥﺎﺤﺘﻣﺍ ﺍﺭ ﻥﺁ ﻥﺎﺗﺩﻮﺧ

<!DOCTYPE html>
<html>
<body>

<h2>Redeclaring a Variable Using let</h2>

<p id="demo"></p>

<script>
let  x = 10;
// Here x is 10

{  
  let x = 2;
  // Here x is 2
}

// Here x is 10
document.getElementById("demo").innerHTML = x;
</script>

</body>
</html>

`const ﻭ var، let ﻦﯿﺑ ﺕﻭﺎﻔﺗ`

	Scope	Redeclare	Reassign	Hoisted	Binds this
var	No	Yes	Yes	Yes	Yes
let	Yes	No	Yes	No	No
const	Yes	No	No	No	No

`؟ﻪﺑﻮﺧ ﯽﭼ`

ﺪﯿﻫﺩ ﻩﺯﺎﺟﺍ ﻭ const

`؟ﺖﺴﯿﻧ ﺏﻮﺧ ﯼﺰﯿﭼ ﻪﭼ`

var ﺩﻮﺷ ﻡﻼﻋﺍ ﺖﺴﯿﻧ ﻡﺯﻻ.

var ﺖﺳﺍ ﻪﺘﻓﺎﯾ ﺶﯾﺍﺰﻓﺍ.

var ﺖﺳﺍ ﻞﺼﺘﻣ ﻦﯾﺍ ﻪﺑ.

`ﺮﮔﺭﻭﺮﻣ ﯽﻧﺎﺒﯿﺘﺸﭘ`

ﺪﻨﺘﺴﻫ const ﻭ let ﯼﺪﯿﻠﮐ ﺕﺎﻤﻠﮐ

:ﺪﻨﮐ ﯽﻣ ﻒﯾﺮﻌﺗ ﺍﺭ ﻞﻣﺎﮐ ﯽﻧﺎﺒﯿﺘﺸﭘ ﺎﺑ ﺮﮔﺭﻭﺮﻣ ﯼﺎﻫ ﻪﺨﺴﻧ ﻦﯿﻟﻭﺍ ﺮﯾﺯ ﻝﻭﺪﺟ


Chrome 49	Edge 12	Firefox 36	Safari 11	Opera 36
Mar, 2016	Jul, 2015	Jan, 2015	Sep, 2017	Mar, 2016

`ﺩﺪﺠﻣ ﻡﻼﻋﺍ`

ﺖﺳﺍ ﺯﺎﺠﻣ var ﺎﺑ ﺖﭙﯾﺮﮑﺳﺍ ﺍﻭﺎﺟ ﺮﯿﻐﺘﻣ ﺩﺪﺠﻣ ﻡﻼﻋﺍ

`ﻝﺎﺜﻣ`

var x = 2;
// Now x is 2

var x = 3;
// Now x is 3

→ ﺪﯿﻨﮐ ﻥﺎﺤﺘﻣﺍ ﺍﺭ ﻥﺁ ﻥﺎﺗﺩﻮﺧ

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript let</h2>

<p>Redeclaring a JavaScript variable with <b>var</b> is allowed anywhere in a program:</p>

<p id="demo"></p>

<script>
var x = 2;
// Now x is 2

var x = 3;
// Now x is 3

document.getElementById("demo").innerHTML = x;
</script>

</body>
</html>

:ﺖﺴﯿﻧ ﺯﺎﺠﻣ ﮎﻮﻠﺑ ﻥﺎﻤﻫ ﺭﺩ ﺮﯿﻐﺘﻣ ﮏﯾ ﺩﺪﺠﻣ ﻡﻼﻋﺍ ،let ﺎﺑ

`ﻝﺎﺜﻣ`

var x = 2;   // Allowed
let x = 3;   // Not allowed

{
let x = 2;   // Allowed
let x = 3;   // Not allowed
}

{
let x = 2;   // Allowed
var x = 3;   // Not allowed
}

:ﺖﺳﺍ ﺯﺎﺠﻣ ،ﺮﮕﯾﺩ ﮎﻮﻠﺑ ﮏﯾ ﺭﺩ ،let ﺎﺑ ﺮﯿﻐﺘﻣ ﮏﯾ ﺩﺪﺠﻣ ﻡﻼﻋﺍ

`ﻝﺎﺜﻣ`

let x = 2;   // Allowed
{
let x = 3;   // Allowed
  }
  
  {
let x = 4;    // Allowed
  }

→ ﺪﯿﻨﮐ ﻥﺎﺤﺘﻣﺍ ﺍﺭ ﻥﺁ ﻥﺎﺗﺩﻮﺧ

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript let</h2>

<p>Redeclaring a variable with <b>let</b>, in another scope, or in another block, is allowed:</p>

<p id="demo"></p>

<script>
let x = 2;   // Allowed

{
  let x = 3;   // Allowed
}

{
  let x = 4;   // Allowed
}
document.getElementById("demo").innerHTML = x;
</script>

</body>
</html>

`ﻥﺩﺮﺑ ﻻﺎﺑ ﻩﺯﺎﺟﺍ`

ﺪﻨﺘﺴﻫ ﻻﺎﺑ ﻻﺎﺑ ﺭﺩ var ﺎﺑ ﻩﺪﺷ ﻒﯾﺮﻌﺗ ﯼﺎﻫﺮﯿﻐﺘﻣ

`ﻝﺎﺜﻣ`

:ﺖﺳﺍ ﺏﻮﺧ ﻦﯾﺍ

 carName = "Volvo";
  var carName;

→ ﺪﯿﻨﮐ ﻥﺎﺤﺘﻣﺍ ﺍﺭ ﻥﺁ ﻥﺎﺗﺩﻮﺧ

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Hoisting</h2>

<p>With <b>var</b>, you can use a variable before it is declared:</p>

<p id="demo"></p>

<script>
carName = "Volvo";
document.getElementById("demo").innerHTML = carName;
var carName;
</script>

</body>
</html>

.ﺪﯿﻨﮐ ﻪﻌﻟﺎﻄﻣ ﺍﺭ Hoisting ﺖﭙﯾﺮﮑﺳﺍ ﺍﻭﺎﺟ ﻞﺼﻓ ،ﺪﯿﻧﺍﺪﺑ ﺮﺘﺸﯿﺑ ﻥﺩﺮﺑ ﻻﺎﺑ ﺩﺭﻮﻣ ﺭﺩ ﺪﯿﻫﺍﻮﺧ ﯽﻣ ﺮﮔﺍ

ﮏﯾ ﻪﺑ ﺮﺠﻨﻣ ﻥﻼﻋﺍ ﺯﺍ ﻞﺒﻗ let ﺮﯿﻐﺘﻣ ﺯﺍ ﻩﺩﺎﻔﺘﺳﺍ :ﯽﻨﻌﻣ

`ﻝﺎﺜﻣ`

carName = "Saab";
let carName = "Volvo";

→ ﺪﯿﻨﮐ ﻥﺎﺤﺘﻣﺍ ﺍﺭ ﻥﺁ ﻥﺎﺗﺩﻮﺧ

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Hoisting</h2>
<p>With <b>let</b>, you cannot use a variable before it is declared.</p>
<p id="demo"></p>

<script>
try {
  carName = "Saab";
  let carName = "Volvo";
}
catch(err) {
  document.getElementById("demo").innerHTML = err;
}
</script>

</body>
</html>