Is there any difference between setting the default value the following ways and which one is correct?

```
1) var1 = var1 || 'default_value'
2) var1 = typeof(var1) !== 'undefined' ? var1 : 'default_value'
3) var1 = var1 !== 'undefined' ? var1 : 'default_value'
4) var1 = var1 != 'undefined' ? var1 : 'default_value'

```