Why can't I assign hash to a variable in javascript?

Question

I need to convert this:

prev = {in_progress: 1, todo: 3, done: 1}

Into this

output = {[ ['Status', 'Count'], ['Todo', 3], ['In Progress', 1], ['Done', 1] ]}

When I'm trying to assign prev to a variable, it gets assigned.

let a = {in_progress: 1, todo: 3, done: 1}

Success.

But when im trying to assign output to a variable, it throws an error

let a = {[ ['Status', 'Count'], ['Todo', 1], ['In Progress', 2], ['Done', 3] ]}

Error: 
Uncaught SyntaxError: Unexpected token ,

Can you explain the reason behind this?

Answer 1

The problem is that {[ ['Status', 'Count'], ['Todo', 3], ['In Progress', 1], ['Done', 1] ]} is not a valid object literal. It's just curly braces around a list of lists. Object literals have to have key: value pairs.

If you wanted to turn it into an object, it would look like { 'Status': 'Count', 'Todo': 3, 'In Progress': 1, 'Done': 1 } .

If you already have the list of lists and want to turn it into an object programmatically, you can do that with reduce :

// Note: no braces
let kvlist = [ ['Status', 'Count'], ['Todo', 3], ['In Progress', 1], ['Done', 1] ];
let obj = kvlist.reduce((h,[k,v]) => { h[k] = v; return h },{});

Answer 2

You could get the entries and map the formatted key with the value.

 const format = s => s.split('_').map(([c, ...s]) => [c.toUpperCase(), ...s].join('')).join(' '); var prev = { in_progress: 1, todo: 3, done: 1 }, result = [ ['Status', 'Count'], ...Object.entries(prev).map(([k, v]) => [format(k), v]) ]; console.log(result);