To open command prompt in your browser press F12 or Ctrl+Shift+I. Here's the full list of in-game commands:

Global Message: boardcast('message_here')

Set Body Color: setColor(colorID)

Set Skill: setSkill(amount)

Set Score: setScore(amount)

Set Player Size: setSize(value)

Set Tank: setTank('export_name') - Tank's export name can be found in definitions.js

Set Stat: setStat('stat_name', value)

Spawn Entity: spawnEntity('export_name', x_position*, y_position*, team_ID*, color_ID*, size*, score*) - Enitity's export name can be found in definitions.js.
*Optional

Teleport: teleport(x_position, y_position)

Set Children: setChildren(amount)

Set Invisibility: setInvisible(fadeInTime, fadeOutTime, limit)

Set Field Of View: setFOV(value)

Set Auto-Spin Speed: setSpinSpeed(value)

Set Entity: setEntity('export_name, size, isMinion = true/false') - Enitity's export name can be found in definitions.js.

Remove Children: clearChildren()

Set Player's Team: setTeam(team_ID) - ID's:
Blue team: 1
Red team: 2
Green team: 3
Pink team: 4

Set Skills: skillSet(atk, hlt, spd, str, pen, dam, rld, rgn, shi)

Rainbow Body Effect Speed: rainbowSpeed(value)

Set Control: setControl(amount)