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Double.NaN Float.NaN

Double.NaN  Float.NaN double i = 0.0/0.0; double i = Double.NaN; equals http://docs.oracle.com/javase/7/docs/api/java/lang/Double.html public boolean equals( Object  obj) Compares this object against the specified object. The result is true if and only if the argument is not null and is a Double object that represents a double that has the same value as the double represented by this object. For this purpose, two double values are considered to be the same if and only if the method doubleToLongBits(double) returns the identical long value when applied to each. Note that in most cases, for two instances of class Double , d1 and d2 , the value of d1.equals(d2) is true if and only if d1.doubleValue() == d2.doubleValue() also has the value true . However, there are two exceptions: If d1 and d2 both represent Double.NaN , then the equals method returns true , even though Double.NaN==Double.NaN has the value ...
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process.env in Node.js

process | Node.js http://nodejs.cn/api/process.html process is a global  object http://nodejs.cn/api/process.html#process_process_env demo in script： if (process.env.NODE_ENV === 'production') { module.exports = require('./prod.js') } else { module.exports = require('./dev.js') } input "node" line commend node > process.env  // show value On Windows: set test=testValue on OS X or Linux: export test=testValue In js file process.env.test= 'dev'; package.json： "scripts": { "start": "set test=dev && node app.js" } ------------------------ Windows environment variant cmd > set test-env   // exit set test-env=production set path=%path%;C:\web;C:\Tools set test-env= my computer -> property -> advance -> environment variant... ---------------------- Linux echo $test-env     //check value of test-env // set value of test-env export test-env=production # attach va...
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