Add Map#loadImage method and Map#addImage examples

[lucaswoj]

This PR:

• exposes ajax#getImage as Map#loadImage for use with Map#addImage
• adds an example using Map#addImage with an external URL
• adds an example using Map#addImage with a procedurally generated image

Launch Checklist

• briefly describe the changes in this PR
• write tests for all new functionality 😬
• document any changes to public APIs
• manually test the debug page

[mourner]

Do you remember why we have es6 env set to false a few lines below? As far as I remember, turning this back to true would allow not specifying common globals like this.

[lucaswoj]

As best I remember we were just to avoid using es6 features with limited browser support. This is less of a concern now. I have enabled the "es6" flag and removed this global in the latest commit.

[jfirebaugh]

We need to continue to write examples without using ES6 features such as let/const or arrow functions (not supported by iOS 9) and for...of (not supported by IE 11). I think it's useful to keep this configuration option to catch accidental uses of these types of features. I suggest we revert the latest commit.

[lucaswoj]

Right -- the examples don't get bubleifyied. I'll revert the last commit and leave a comment about this in the eslint file.

[mourner]

@jfirebaugh as far as I remember, the env switches are only for predefined globals like Uint8Array — they're not used for catching keywords like let.

[jfirebaugh]

Yeah, you're right. And "parserOptions": { "ecmaVersion": 5 } doesn't work either. 😞

[mollymerp]

Thanks for putting these together @lucaswoj!
These look great, but I wonder if we could make our terminology more consistent/clear? Should the methods themselves be called "addSprite" (I realize it's a little late to be making this suggestion 😬)? and should these examples refer to sprites instead of icons?

icon- specifically refers to symbol layers in the style-spec, but these icons can also be used by -pattern layers as well, right?

[lucaswoj]

@mollymerp There's a bunch of context on the naming decisions here: mapbox/mapbox-gl-style-spec#220 (comment) and #2059 (comment)

There's a case to be made that these examples should be titled "Add an image to the map" but I think the current names will best direct those looking for this functionality.

[mollymerp]

🐑