The same way anyone learns! Most "designer" focused ones are no different, they just have more "it's okay, you're smart too" language. That said, here's a few good resources for beginners:

• Javascript for cats
• Learn Javascript Properly

I found codecademy's Javascript course pretty useful, and this GitHub repo for Must-Watch JavaScript.

I would recommend the Full-stack Javascript Track on Treehouse. The courses are very visual and they focus on playing with the DOM rather than high-level Javascript concepts.

Simple, interactive, and plenty of insightful exercises: http://eloquentjavascript.net/

I would recommend Udacity course

Not targeted for UXUI designers, but for anyone who doesn't know JavaScript. In my opinion the best material to start learning JavaScript.

How to learn JavaScript properly

the best resource I know is David Flanagan's book http://www.amazon.com/JavaScript-Definitive-Guide-Activate-Guides/dp/0596805527

Learn Code Academy on Youtube is fantastic.

I'd echo a bunch of the comments here. I also suggest diving in and trying to code an interface such as GMail. I've always found that I learned more by coding and running into roadblocks vs going through a course.

I think this is still the best resource for learning from the ground up: http://javascriptbook.com

I think that the best way to learn is with flow diagram, because is very useful visual help. By example learn the sentence: if..else: http://www.tutorialspoint.com/javascript/javascript_ifelse.htm

This may be a little more niche, but the GSAP (greensock.js) course over at ihatetomatoes.com is a fantastic foray into javascript animation. I found that learning javascript in an animation context gave me a satisfaction with every new line of code that helped the concepts really sink in to my designer brain.

http://bit.ly/1KfLu1D

I love Human Javascript from one of the AmpersandJS core members.

When you say "specifically for UI/UX designers"? Do you mean a course with UI-oriented examples?

Bookmarked.

How much do you know already? What are you hoping to target with the "crafted specifically for UI.UX Designers" distinction?

I don't consider this at all tailored for designers, but Code School has well crafted JavaScript courses. They also have HTML and CSS courses that includes a "Fundamentals of Design" course.

From the author of "You don't know JS." https://www.pluralsight.com/courses/advanced-javascript

If you are a visual learner like me, my money is on a pluralsight subscription for as long as you need to watch the courses you need. They have the most professional and technically in-depth courses you could want that go from beginner to pro.

I recommend JavaScript: Understanding the Weird Parts