javascript - What is this communicating: my_var = my_var || 69 -

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i saw in javascript example

my_var = my_var || 69 

i assume means check if my_var exists, if not set my_var 69. case? there documentation on this, hard represent google/so search, point me in direction of docs or duplicate qa?

(the example didn't use 69, that's me being crass)

easy enough try in js console.

var my_var my_var = my_var || 69 //69  var my_var = 5 my_var = my_var || 69 //5 

you setting variable if carrying falsy value.

falsy values in js are:

1. false
2. null
3. undefined
4. the empty string ''
5. the number 0
6. the number nan