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Execute this code
var x = prompt("Enter a number to test if it is in the range supported by JavaScript.") if (isNaN(x)) { alert('"' + x + '" is not a number.') } else { if (isFinite(x)) { alert('"' + x + '" is a valid number.') } else { alert('"' + x + '" is a number outside the supported range.') } }