How to capitalize the first letter of a var in p5.js

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How to capitalize the first letter of a var in p5.js
I am building a weather forecast site using JavaScript's framework p5.js. I have a description about what's the weather like (ex. few clouds) but the problem is that the api I'm using has only lowercase description. I wan't them to be uppercase but i don't know how to capitalize them. Can somebody help me?
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