ToNumber
true becomes 1 and false becomes 0. undefined becomes NaN, but (curiously) null becomes 0
Objects (and arrays) will first be converted to their primitive value equivalent, and the resulting value (if a primitive but not already a number) is coerced to a number according to the ToNumber rules just mentioned.
To convert to this primitive value equivalent, the ToPrimitive abstract operation (ES5 spec, section 9.1) will consult the value (using the internal DefaultValue operation -- ES5 spec, section 8.12.8) in question to see if it has a valueOf() method. If valueOf() is available and it returns a primitive value, that value is used for the coercion. If not, but toString() is available, it will provide the value for the coercion.
SRE实战 互联网时代守护先锋，助力企业售后服务体系运筹帷幄！一键直达领取阿里云限量特价优惠。If neither operation can provide a primitive value, a TypeError is thrown.
