JavaScript const

February 8, 2021 10:45 am IST

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JavaScript const

The const is a JavaScript keyword for defining variables that are prevented from being updated.

Note: The const does NOT define a constant value. It defines a constant reference to a value, i.e., we cannot change constant primitive values, but we can change the properties of constant objects.

Update const

Note: The following example will throw an error as we are trying to update the value which is declared with const keyword.

Example

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<!DOCTYPE html> <html> <body> <script> const x = 1; x = x + 1; document.write("x = "+x); </script> </body> </html>

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Re-Assign const

Note: The following example will throw an error as we are trying to re-assogm the value which is declared with const keyword.

Example

HTML Online Editor

<!DOCTYPE html> <html> <body> <script> const x = 1; x = 1; document.write("x = "+x); </script> </body> </html>

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Add / Change / Delete Property in Object const

Note: The following example will NOT throw an error as we are trying to change the properties of constant objects.

Example

HTML Online Editor

<!DOCTYPE html> <html> <body> <script> const bike = {company:"Honda", model:"CBR 1000RR"}; //Add property bike.color="Red"; //Change property bike.model="Gold Wing"; //Delete property delete bike["company"]; document.write("I went to "+bike.company+" Showroom"); document.write("<br>I purchased "+bike.model); document.write("<br>Which is "+bike.color+" in color"); </script> </body> </html>

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Trying to Re-Assign Object const

Note: The following example will throw an error as we are trying to change the object itself.

Example

HTML Online Editor

<!DOCTYPE html> <html> <body> <script> const bike = {company:"Honda", model:"CBR 1000RR"}; bike = {company:"Harley Davidson", model:"Fat Bob"}; document.write("Company = "+bike.company); </script> </body> </html>

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