Converted docs/documented-method.js to ES6

[abhinavsagar]

Part of #3758

[abhinavsagar]

@stalgiag Should the codebase itself be converted to ES6 ?

[stalgiag]

Hi @abhinavsagar thanks for the offer but most of this conversion was handled by #3874. That said there will likely be further slight modifications that might need help. Feel free to follow open issues such as #3877 and #3875 to see if there are any new todos about ES6 conversion.

[stalgiag]

I think that #3877 in particular is relevant to this particular PR. Definitely the change from var will make sense but we may use const instead of let for this type of variable.

[abhinavsagar]

Thanks. I will go through the open issues.