Fix modeBarButtons issue

[nickmelnikov82]

Fixes dash issue #1157
As @alexcjohnson wrote:

The problem is here where we mutate the input - which is the user-provided array, something we should not alter. Instead we should create a copy with the object inserted in place of the string. Would be a one-line change if we used ramda in plotly.js, but we don't...

[archmoj]

Thanks very much for the PR.
Please note that lodash is a dev-dependency.
And for various reasons (e.g. size & potential security issues) we are not interested to include that in our bundles.
Alternatively you could use

var extendDeep = require('../../lib').extendDeep;

and then

var customButtons = extendDeep([], context.modeBarButtons);

Or perhaps even better would be to use extendFlat if possible?

[nickmelnikov82]

Fixed. Using the extendFlat function is not possible because the object has a nested structure.

[archmoj]

Please add a test here:

plotly.js/test/jasmine/tests/modebar_test.js

Line 158 in 042742d

describe('creates a custom button', function() {

Also I appreciate if you draft 6177_fix.md as described here:
https://github.com/plotly/plotly.js/blob/master/.github/PULL_REQUEST_TEMPLATE.md

Thank you!

[archmoj]

Suggested change

	- Fix modeBarButtons mutate the input, issue [[#1157](https://github.com/plotly/dash/issues/1157)]
	- Fix custom modebar buttons mutate the input [[#6177](https://github.com/plotly/plotly.js/pull/6177)]

[archmoj]

This deep copy appears to be needed in the first case only.
I suggest you revert the change here and move deep copy inside fillCustomButton function.
For example:

function fillCustomButton(inButtons) {
  var customButtons = extendDeep([], inButtons);
  ...

[archmoj]

Thanks very much for the PR.
💃