most frequently occurring character

Question

Given a non-empty string, return the most frequently ocurring character.

If there are multiple characters with same occurrance, return an array of them.

count('abbccc')
// 'c'

count('abbcccddd')
// ['c', 'd']

Follow-up: What is the time & space complexity of your approach?

Code

/**
 * @param {string} str
 * @returns {string | string[]}
 * /
function count(str) {
  // your code here
}

Source

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